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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Investigating Symbolic Capabilities of Large Language Models</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Neisarg Dave</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Daniel Kifer</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>C. Lee Giles</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ankur Mali</string-name>
          <email>ankurarjunmali@usf.edu</email>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>College of Information Sciences and Technology, The Pennsylvania State University</institution>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Department of Computer Science and Engineering, The Pennsylvania State University</institution>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Department of Computer Science and Engineering, University of South Florida</institution>
          ,
          <country country="US">USA</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Prompting techniques have significantly enhanced the capabilities of Large Language Models (LLMs) across various complex tasks, including reasoning, planning, and solving math word problems. However, most research has predominantly focused on language-based reasoning and word problems, often overlooking the potential of LLMs in handling symbol-based calculations and reasoning. This study aims to bridge this gap by rigorously evaluating LLMs on a series of symbolic tasks, such as addition, multiplication, modulus arithmetic, numerical precision, and symbolic counting. Our analysis encompasses eight LLMs, including four enterprise-grade and four open-source models, of which three have been pre-trained on mathematical tasks. The assessment framework is anchored in Chomsky's Hierarchy, providing a robust measure of the computational abilities of these models. The evaluation employs minimally explained prompts alongside the zero-shot Chain of Thoughts technique, allowing models to navigate the solution process autonomously. The findings reveal a significant decline in LLMs' performance on context-free and context-sensitive symbolic tasks as the complexity, represented by the number of symbols, increases. Notably, even the fine-tuned GPT3.5 exhibits only marginal improvements, mirroring the performance trends observed in other models. Across the board, all models demonstrated a limited generalization ability on these symbol-intensive tasks. This research underscores LLMs' challenges with increasing symbolic complexity and highlights the need for specialized training, memory and architectural adjustments to enhance their proficiency in symbol-based reasoning tasks.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Large Language Models</kwd>
        <kwd>Symbolic Tasks</kwd>
        <kwd>Chomsky's Hierarchy</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>Large language models are driving revolutionary advancements in artificial intelligence. They are
transforming how we interact with and interpret data across various modalities. These models have
surpassed human performance in generating text, images, and videos. LLM-augmented systems are
revolutionizing traditional expert systems such as search, retrieval, theorem proving, symbolic reasoning,
programming, and drug discovery. Amid these advancements, exploring the symbolic capabilities of
LLMs, particularly in logical reasoning, mathematical computation, and formal language manipulation,
remains a crucial area of investigation.</p>
      <p>
        A key aspect of leveraging LLM capabilities is developing efective prompting techniques. Prompts
are carefully designed inputs that guide the model’s behavior, enabling it to perform specific tasks or
exhibit desired behaviors. These techniques include few-shot and zero-shot learning, where models
are prompted with examples or instructions to help them generalize to new tasks without extensive
retraining. Other techniques include Chain-of-Thought [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ], Tree-of-Thought [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], Graph-of-Thought
[
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] etc. While LLMs have gained prominence, other neural network models have also been studied for
their symbol manipulation abilities. This research can be broadly categorized into two areas: directly
learning to solve logical and mathematical problems, and research conducted from the perspective
of formal methods and automata theory. Recurrent Neural Networks (RNNs) are highly eficient at
learning regular grammars, with Second Order RNNs particularly adept at encoding stable states.
Memory-augmented models, such as stack-RNN, tape-RNN, and Neural Turing Machines (NTMs),
have demonstrated their ability to handle more complex languages. Additionally, transformers, with
their attention mechanisms, have been explored for their potential in managing formal languages and
symbolic computations. However, RNN-based models often fail to generalize on tasks such as math
word problems and logical reasoning.
      </p>
      <p>In this work, we address the symbol manipulation capabilities of Large Language Models (LLMs). We
investigate fundamental mathematical operations such as addition, multiplication, and counting. The
inherent complexity of these tasks is derived from Chomsky’s Hierarchy. Specifically, we present the
following research questions:
RQ1: Can LLMs apply simple symbolic rules, such as addition and multiplication, stably and repeatedly?
RQ2: How precisely can LLMs preserve the construction of a group of symbols and respect the order
of operations?</p>
      <p>
        In this study, we first discuss task complexity and the computational requirements necessary to solve
these tasks. We then estimate the number of bits required to encode such a machine and compare it to
the knowledge tuple encoding in LLMs as described by Deletang et al. [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. Additionally, we estimate the
number of parameters needed for a neural network to solve the given tasks using both methods. Finally,
we provide experimental evidence of the performance of LLMs. We evaluate four enterprise LLMs and
four open-source LLMs on three essential skills: addition, multiplication, and counting, and design 5
tasks to answer 1 and 2. Utilizing Hindu-Arabic numerals and both uppercase and lowercase
English alphabets as symbols, we construct multi-digit numbers from single digits. This approach
allows us to assess the precision of the LLMs by increasing the number of digits in the numbers, both
before and after the decimal point.
      </p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>
        Early research demonstrated that recurrent neural networks (RNNs) could learn and encode deterministic
ifnite state automata, enabling them to perform symbolic tasks such as rule-based reasoning and
grammatical inference. Omlin and Giles [
        <xref ref-type="bibr" rid="ref5">5, 6, 7</xref>
        ] demonstrated the extraction, insertion, and refinement
of deterministic finite automata in recurrent neural networks. They also explored higher-order recurrent
networks and their applications in grammatical inference [8]. However, RNNs have been shown to
struggle with tasks extending beyond regular grammars. For instance, RNNs require auxiliary data
structures like stacks or tapes to process inputs governed by context-free or context-sensitive grammars.
Mali et al. [9, 10] and Stogin et al. [11] advanced this work by providing theoretical bounds for the
expressiveness of RNNs and memory-augmented RNN models. Dave et al. [12] empirically showed that
second-order connections encode states more stably for formal languages in comparison to first-order
RNNs like LSTM and GRU. Symbolic tasks encompass a range of applications, including the manipulation
of formal languages and the execution of mathematical operations [13]. Mathematics provides a
structured framework for symbolic evaluation, aligning well with the principles of neurosymbolic AI,
where symbol manipulation and operations are central.
      </p>
      <p>Saxton et al. [14] created a dataset of math questions across various topics and observed that LSTM
models barely memorized the question-answer pairs and could not generalize. Dave et al. [15] used the
same dataset to create distractors for math multiple-choice questions. Mistry et al. [16] summarized
the specialized architectures developed to solve arithmetic tasks, highlighting gaps in the robustness,
compositionality, and interpretability of these models. The development of large language models
(LLMs) has spurred significant interest in their mathematical and symbolic capabilities. Research has
increasingly focused on training LLMs specifically for mathematical tasks, aiming to enhance their
proficiency in symbolic reasoning. LLM models like Deepseek [ 17], LLemma [18], and Metamath
[19] are specially trained with math datasets. However, studies have shown that neural networks,
including LLMs, often fail to genuinely learn to solve mathematical and symbolic tasks. Dziri et al.
[20] investigated the limitations of LLMs across three problems: multiplication, puzzle solving, and
dynamic programming. They tested GPT-3, GPT-3.5, and GPT-4 models using zero-shot, few-shot, and
ifne-tuning techniques, revealing a significant decline in performance as the sample size increased.
Similarly Shakarian et. al. [21] also reported performance of ChatGPT [22] declines with the increase
in the number of addition and subtraction operations required to solve math word problems (MWPs).
Furthermore, they also observe that LLMs perform much better when asked to show work. Additionally,
Frieder et al. [23] demonstrated that GPT-4’s mathematical proficiency was far below graduate-level
standards. Previous research on the mathematical proficiency of large language models (LLMs) has
primarily focused on a broad set of math problems and reported findings based on static datasets such
as GSM 8K [24] and MATH [25]. This approach does not uncover the underlying inconsistencies in
LLMs’ understanding of mathematics. In this work, we examine the consistency and precision of LLMs
as the complexity of the tasks increases.</p>
      <p>Through our analysis, we assess the performance of enterprise and open-source LLMs trained on
text and mathematical datasets, testing them on five symbolic tasks. These tasks fall into context-free
and context-sensitive categories on Chomsky’s hierarchy. We discuss the bit complexity of encoding
symbolic tasks as an automaton and a set of knowledge tuples. Our experiments show that while
enterprise LLMs, with their higher parameters and curated datasets, outperform open-source models,
all models exhibit similar performance trends that align with the knowledge-tuple encoding of symbolic
tasks. Fine-tuning these models on symbolic tasks has little efect on their performance, indicating that
LLMs do not learn the rules of symbol manipulation but rather encapsulate relationships in terms of
tuples. The contrast in the number of parameters required to encode symbolic tasks suggests a need for
developing larger models capable of learning automata rather than merely storing information.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Background</title>
      <p>
        Ideally, a model should either encode mathematical tasks as knowledge tuples or learn to simulate a
machine that can solve such tasks eficiently. In this section, we examine the parameters required by
models using both approaches. We relate tasks to their complexity, derived from Chomsky’s hierarchy,
with detailed definitions provided in the appendix. Furthermore, prior work by Allen-Zhu et al. [
        <xref ref-type="bibr" rid="ref6">26</xref>
        ]
has studied the bit capacity of large language models. Following their setup, we use the conversion of 2
bits per parameter to estimate the number of parameters required.
      </p>
      <sec id="sec-3-1">
        <title>3.1. Addition of Sequence of Numbers</title>
        <p>A finite state machine can add two numbers. Addition of sequence of numbers can be represented by
production rules  → ;  → , where is the sequence of numbers,  is the sum of partial sequence
and  is the remaining sequence. It is clear from the construction that a non-deterministic PDA can
solve this problem. At each step of operation, the nPDA computes the sum of two numbers of arbitrary
but finite number of digits. Let the the number of digits be  and . Then the number of digits in the
sum of two numbers is (, ) + 1. There are two ways a LLM can encode the the rules of addition
: 1) Encoding the states and stack in the internal parameters of the model, 2) Encoding addition rules for
each pair of numbers. Encoding the nPDA requires 2(#(  ) +   ()) bits
which is considerable lower than encoding specific addition rules for numbers of arbitrary number of
digits.</p>
        <p>Proposition 3.1. For the addition of two base  numbers with finite digits  and , respectively, where
 ≥ , the encoding of their sum requires at most (2 +  + 1) log2  bits. This account includes the
possibility of a carryover in the addition, which may increase the length of the resulting number by one
digit.</p>
        <p>Proof. Consider two numbers  and  represented in base , where  has  digits and  has  digits
with  ≥ . Each digit in these numbers requires log2  bits to encode due to the need to distinguish
between  diferent values.</p>
        <p>Step 1: Encoding Individual Numbers.</p>
        <p>• The number  requires  log2  bits.</p>
        <p>• The number  requires  log2  bits.</p>
        <p>Step 2: Maximum Size of Sum. When adding  and , the maximum number of digits in the sum,
 =  + , could be  + 1 (considering the possibility of a carryover from the most significant digit).</p>
        <p>Step 3: Encoding the Sum. The sum  hence requires at most ( + 1) log2  bits.</p>
        <p>Step 4: Total Encoding Requirement. Adding the encoding requirements together, the total
number of bits needed is:</p>
        <p>log2  +  log2  + ( + 1) log2  = (2 +  + 1) log2 .</p>
        <p>This calculation confirms that the sum of the encoding requirements for the numbers and their potential
maximum sum, considering carryover, matches and proves the proposition.</p>
        <p>Corollary 3.2. Consider a sequence of  numbers, each of base 10 and with at most  digits. To
completely memorize all possible addition operations within this sequence, a Large Language Model (LLM)
must store at least  (3max − 2) log2 10 bits of information, where:</p>
        <p>max = ⌊︀ 1 + log10 (︀ (10 − 1) ·  )︀⌋ ,
and</p>
        <p>( + 1)
  = 4 ,  =  (10 − 1)
representing the total number of distinct pairwise addition operations that could be required to solve the
sequence. Here, max represents the maximum number of digits in any number or partial sum within the
given sequence, and   quantifies the total number of unique addition rules required for comprehensive
solution strategies.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Multiplication</title>
        <p>Multiplicating two numbers of arbitrary digits is a context-sensitive task. It requires a finite state
machine augmented with a finite tape. For the input expression of form  ×  on the input tape, the
tape pointer reads the digits of  from right to left. For digit  with place value  in , the pointer moves
right to the output part of the tape and increments it  *  *  times. The pointer moves back to the
digit, sets it to &lt;BLANK&gt;, and moves to the digit on the left.</p>
        <p>Proposition 3.3. An automaton, which includes a finite state controller and a finite length tape, capable
of computing the multiplication of an -digit number and an -digit number, requires encoding with
log2 6 + 2 · ( + ) · log2  bits.</p>
        <p>Proof. To compute the multiplication of two numbers, each represented by  and  digits respectively,
consider an automaton designed as follows:</p>
        <p>State Design: The finite state controller is structured with six distinct states to manage the
computation:
1. Two states are dedicated to reading the digits of the numbers, specifically one state for each
number (1 and 2).
2. One state is allocated for writing the output of the multiplication.
3. Three additional states facilitate the movement of the tape head to the appropriate positions
corresponding to the digits of the two numbers and the resulting output.</p>
        <p>Tape Complexity: The tape must accommodate the digits of both numbers and the resultant product.
The maximal length of the product of two numbers, each with  and  digits, is  +  digits. Therefore,
the tape’s length is approximately (2 · ( + )) to account for both input numbers and their maximal
output size.</p>
        <p>Bit Encoding: The number of bits required to encode the state machine is determined by the logarithm
of the number of states, giving log2 6 for the states. The tape encoding requires 2 · ( + ) · log2 
bits, where log2  bits are needed to encode each digit of the input and output numbers, assuming the
numbers are in base .</p>
        <p>Combining these components, the total encoding requirement for the automaton is thus:
log2 6 + 2 · ( + ) · log2  bits.</p>
        <sec id="sec-3-2-1">
          <title>This completes the proof.</title>
          <p>Proposition 3.4. Given two integers  and , where  is an -digit number and  is an -digit number
in base , a multiplication rule that expresses the relationship  ×  =  can be encoded as a knowledge
tuple (, ,  ). This tuple can be stored using at most 2( + ) log2  bits.</p>
          <p>Proof. The multiplication of  and  results in  , where  can have at most  +  digits (considering
the maximum carry-over in base ):
• Each digit of  and  can be encoded using log2  bits because each digit represents a value from
0 to  − 1.
• Therefore,  requires  · log2  bits and  requires  · log2  bits.</p>
          <p>• The product  can be as large as  +  digits, thus requiring at most ( + ) · log2  bits.</p>
          <p>The knowledge tuple (, ,  ) encapsulates the complete multiplication expression and therefore
combines the storage requirements of , , and  . Thus, the total bit requirement is the sum of the bits
needed to store , , and  :</p>
          <p>2( + ) log2  bits,
assuming the maximum possible size for  and ignoring potential savings from compressing common
information between , , and  . This completes the proof.</p>
          <p>Corollary 3.5. Given all possible tuples (, ,  ) where  and  are numbers in base 10 with a maximum
of max digits, these tuples can be encoded in a Large Language Model (LLM) using at most
4max · 102max · log2 10 bits,
where max is the maximum number of digits in any number among , , and  .</p>
          <p>Proof. To encode each of the tuples (, ,  ) where  and  are up to max digits:
1. The total number of possible values for  or  is 10max , since each digit can range from 0 to 9.
2. The product  =  ×  can have at most 2max digits (considering the worst-case scenario of
multiplication).
3. Thus, the number of possible tuples (, ,  ) is 10max × 10max × 102max = 104max .
4. Each tuple then requires encoding that can be estimated by calculating the total number of bits
to represent each digit of , , and  in binary:</p>
          <p>4max · log2 10 bits per digit × 102max possible tuples.</p>
          <p>This provides upper bound on the bit requirement to encode tuples in an LLM.</p>
        </sec>
      </sec>
      <sec id="sec-3-3">
        <title>3.3. Symbolic Counting</title>
        <p>Counting the frequency of a character  in a given string  is well solved using an automaton equipped
with a counter and a register. Let  be the set of all possible characters s.t.  ∈  and  ∈  * . First, the
automaton reads  and stores it in the register. The finite state controller then reads characters ′ ∈ 
step by step and increments the counter when ′ = .</p>
        <p>Proposition 3.6. An automaton capable of counting the frequency of a character in a given string can be
encoded in at most 23 + 2| | + ⌊1 + log ⌋ * log2  bits, where  is the maximum length
of an input string in base 
Proof. Step 1 : Encoding the states: The above discussed automaton can function with 3 states. The
automaton starts in state 0, reads the character  into the register, and moves to the next state (1). The
automaton now reads the string, one character at a time. If the input character matches the character in
the register, the automaton moves into state 2. Otherwise, it remains in 1. The states {0, 1, 2}
can be encoded in log2 3 bits.</p>
        <p>Step 2 : Encoding the register : Since the register holds one character  ∈  , it can be encoded in
2| | bits.</p>
        <p>Step 3: Encoding the counter: The maximum value the counter would need to hold is the length
of the longest string. Thus counter can be encoded in ⌊1 + log ⌋ * log2  bits.</p>
        <sec id="sec-3-3-1">
          <title>LLMs can mimic this behavior by encoding knowledge tuples (, , )</title>
          <p>Proposition 3.7. The knowledge tuple (, , ), where  is the frequency of  in  can be encoded in
atmost ( + 1)2| | + ⌊1 + log ⌋ * log2  bits.</p>
          <p>Corollary 3.8. An LLM can encode the entire sample space of (, , ) knowledge tuples of maximum
string length (in base 10) in atmost | |+1Δ, where</p>
          <p>Δ = ( + 1)2| | + ⌊1 + log10 ⌋ * log2 10</p>
          <p>Encoding the entire space of possible string combinations is a gargantuan task. It’s very ineficient,
even for massive LLMs. Especially when counting can be reduced to the addition of a sequence of ones
and zeros, where 1 represents a character match and 0 represents no match. This reduces symbolic
counting into a two-step process:</p>
          <p>Step 1: Using attention mechanism to reduce the character matching problem to a binary sequence
that represents a match. This can be encoded in atmost  + ( + 1)2| | bits.</p>
          <p>Step 2 : Perform sum of sequence on the sequence of 1s and 0s. There will be total of 2
knowledge tuples to encode addition in form (, 1,  + 1) and (, 0, ). These can be encoded in almost
2 * (1 + 2⌊1 + log10 ⌋ log2 10) bits.</p>
          <p>Thus, the bits required by LLMs to encode symbolic counting are:</p>
          <p>+ ( + 1)2| | + 2 * (1 + 2⌊1 + log10 ⌋ log2 10)</p>
        </sec>
      </sec>
      <sec id="sec-3-4">
        <title>3.4. Parameter Estimation</title>
        <p>Based on the estimates discussed above, we now find out the computational capacity of large language
models with respect to the tasks of addition, multiplication, and counting. Table 1 reflects the bound on
input size for given tasks for a model of 7B and 180B parameters, respectively. These bounds are much
closer to the performance that we observe in our experiments. Most LLMs are trained on multiple tasks
and are primarily focused on modeling language rather than symbolic tasks. Hence, our results show
that LLM performance degrades for sample sizes that are way smaller than the bounds discussed.</p>
        <p>Table 2 shows the number of parameters required for the two encoding systems for a fixed input size
on the given tasks. It is observed that, if neural network models could simulate the machines to solve
the task, they would require considerably less number of parameters. Current LLMs have parameters
more aligned with the knowledge tuple encoding system.</p>
        <p>Task
Sum of Sequence
Multiplication
Symbolic Counting</p>
        <p>Size Parameter 7B
Sequence Length 363
#(1) + #(2) 8
String Length 1e8</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Experimental Setup</title>
      <p>Fundamental mathematics operations, like addition and multiplication, are well understood as symbolic
operations. Numbers can be represented as composite symbols composed of a pre-defined set of symbols,
i.e., 0 − 9 numerals. We analyze the performance of large language models on varying dificulty of the
tasks modeled as the input size. All models are tested on 100 samples for each dificulty level. We keep
a consistent seed for data generation to ensure a fair comparison.</p>
      <sec id="sec-4-1">
        <title>4.1. LLM Models</title>
        <p>We conduct our experiments on eight LLM models, including four enterprise models and four
opensource models. The enterprise models are GPT-3.5 (gpt-3.5-turbo-0125), GPT-4 (gpt-4-0125-preview),
Gemini (gemini-pro-1.0), and Claude (claude-3-haiku-20240307). The open-source models analyzed
are Llamma 2 (13B), Llemma (7B), Deepseek (7B), and MetaMath (7B). All open source models except
Llamma-2 13B are pre-trained on math tasks. Llemma 7B is Llamma-7B based model fine tuned on
math datasets. MetaMath is fine-tuned on Llemma-7B. Deepseek is trained on math datasets like
OpenWebMath.</p>
        <p>Model query parameters We keep the maximum token size of 4096 for all models. All models
are queried with temperature of 0 to maximize determinism in the generated text. Models are not
given access to any external API’s, python interpretter, documents or databases, to ensure analysis of
standalone LLM performance. No examples are provided in the prompt, and single prompt query is
used for each input sample. Zero-shot COT method is used to allow models to navigate the problems
without any help.</p>
        <p>Prompting All prompts are composed of two components: system prompt and user prompt. Gemini
API does not have separate fields for system and user prompts, hence we concatenate both. System
prompt is composed of the following components:
1. Identity - e.g. for sum of sequence, the prompt stats with "You are number crunching machine..."
2. Input type - the input type can be sequence of numbers, arithmetic expression etc.
3. Command - instruction on what to do with the input. e.g. calculate the sum
4. Constraint [Optional] - Any extra guideline or constraint for the model, e.g. Treat the upper and
lower case characters as separate
5. Zero-Shot COT - To help models present the intermediate thoughts and reasoning without
providing any example, we use Zero-shot-COT method. This is done by appending Let’s think
step by step, at the end of the prompt.</p>
        <p>The user prompt has two parts : 1) input identifier and 2) input sequence</p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Symbolic Tasks</title>
        <p>Task
Sum of Sequence
Multiplication
Symbolic Counting
Modular-10 Arithmetic
Decimal Arithmetic</p>
        <p>Categorization by Chomsky’s Hierarchy
Sum of sequence od multi-digit numbers
can be constructed as:
 → ;  → 
Hence it is a context free task
Multiplication of two multi-digit numbers
is a context-sensitive task as
it requires a bounded tape to
perform the operation.</p>
        <p>Counting the matches of a character
in a string requires a counter with a FSM,
A modular arithmetic expression
with brackets require a stack
to store intermediate results and
is thus context-free task
Decimal Arithmetic requires a tape to
perform multiplication and thus is
context-sensitive.</p>
        <p>Machine
Pushdown Automata</p>
        <p>Linearly Bounded</p>
        <p>Automata
Counter Automata
Pushdown Automata</p>
        <p>Linearly Bounded</p>
        <p>
          Automata
1. Sum of Sequence The model is tasked with computing the sum of the sequence of numbers. The
numbers in the sequence are sampled uniformly in the range 10—99. Task dificulty is modeled
as the length of input sequences. We test the sequence of sizes 5, 10, 20, 50, 100, 200, and 500.
2. Modulo-10 Arithmetic While Deletang et al. [
          <xref ref-type="bibr" rid="ref4">4</xref>
          ] used modulo-5 arithmetic to benchmark RNN
and Transformer models. We follow a similar approach and analyze LLMs’ performance on
modulo-10 arithmetic expressions. The expressions are composed of the following operations:
addition, subtraction, multiplication, and brackets. The dificulty of the task is modeled as the
length of expression. We test LLMs with expressions of length 5, 10, 20, 50, 100, 200, 500, 1000,
and 2000.
3. Decimal Arithmetic We test the precision handling capacity of LLMs by introducing decimal
numbers in arithmetic expressions. The dificulty in task is modeled as the number of digits in the
fractional part of decimal, while keeping one digit in whole number part. We test the expressions
with 1, 2, 3, 4, 5, and 6 fractional digits,
4. Multiplication This tests LLM models on the multiplication of 2 whole numbers. The dificulty in
task is modeled as the sum of number of digits in multiplier and the multiplicand. Multiplication
with combined digits of 2, 4, 6, 8, 10, and 12 are tested.
5. Symbolic Counter The LLMs are tested on their ability to count the number of character matches
in a string. The dificulty of task is modeled as the length of string. We test LLMs on string
lengths on 5, 10, 20, 50, 100, 200, 500, 1000, and 2000
        </p>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Fine Tuning</title>
        <p>We fine-tune GPT3.5 model on sum of sequence and symbolic counting tasks. For sum of sequence we
ifne-tune specifically for sequence lengths 5, 10, 20, 50 and 100 with 300 samples for each seq length.
The validation set is composed of 50 samples for each length. Finally the model is tested on all sequence
lengths i.e, 5, 10, 20, 50, 100, 200, and 500 with 100 samples for each length. Similarly, for the symbolic
counting tasks, the model is fine-tuned with strings of length 50, 100, 200, and 500, with 300 for each
length. The model is tested for all lengths with 100 samples each.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Results and Discussion</title>
      <p>Figures 1 - 6 show the performance of LLMs on the five symbolic tasks. In all cases, we can see
that performance starts degrading as the dificulty of input samples increases. By comparing these
results with tables 1 and 2 we can see that performance starts degrading for far simpler examples than
anticipated. This indicates that LLMs have not learned to solve symbolic problems but rather have a
notion of input-output pairings. From the figures, we can see that while GPT3.5 and Claude Haiku
models perform very similarly in all tasks, Gemini is able to sustain performance longer than the other
models on the sum of sequence task while it is usually behind other models in the rest of the tasks.
GPT4 outperforms other models in modulo-10 arithmetic, decimal arithmetic, and multiplication tasks
while lagging behind in other tasks. Claude Haiku performs fairly consistently in all tasks, being the
smallest of all enterprise models. Out of all models, Lemma 7B is the worst-performing model across all
tasks. Deepseek and MetaMath perform slightly better due to their math pre-training.</p>
      <p>In computational tasks, the dificulty is often represented by a parameter that increases the operations
in the corresponding state machine without altering the accepted transitions or the number of states.
Typically, longer strings are considered more dificult. However, this parameterization does not change
the machine’s construction, so a neural network capable of emulating the machine should produce
correct outputs regardless of input length. While memory and precision constraints provide an upper
bound on the input length, modern computers have bounds significantly higher than those used in this
study. For instance, in multiplication, increasing the number of digits in the operands necessitates more
single-digit multiplications and additions. This requirement, however, does not alter the fundamental
operations of multiplication or addition. We represent this complexity with a single parameter: the
combined number of digits in both operands. Our experiments indicate that large language models
(LLMs) fail to maintain accuracy as the number of digits in the operands increases.</p>
      <p>Enterprise and Open Source Models Multiplication is the only task where open-source models
and enterprise models start with similar performances. In symbolic counting, the Llamma 13B model
performs similarly to enterprise models for strings of length 5. In all cases, the performance of
opensource models degrades much faster than that of enterprise models. In the other three tasks, open-source
models perform far below enterprise models, even for simpler cases. An argument could be made that
open-source models are smaller than the enterprise models tested in this work. This further indicates
that performance is highly dependent on the models’ size, making the knowledge-tuple encoding
hypothesis much stronger.</p>
      <p>Math trained models Out of the three math-trained models, Deepseek gives the best overall
performance. However, even math-trained models are not able to sustain their performance on larger
examples. Symbolic counting is the only task where the Llamma 13B model outperforms math-trained
(a) GPT 3.5 fine-tuned on Sum of Sequence (b) GPT 3.5 Fine-Tuned on Symbolic Counter</p>
      <p>Task task
models. All math-trained models have the number of parameters of Llamma 13B.</p>
      <p>Efect of fine tuning Figure 6 shows the comparison of vanilla and fine-tuned GPT3.5 models
on the sum of sequence and symbolic counting tasks. We can observe that fine-tuning has helped
performance in smaller examples but made larger examples a little worse. Overall, all fine-tuning and
closing performances follow vanilla performance, and there is no improvement in the generalization of
the tasks.</p>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusion</title>
      <p>In this work, we analyze the performance of enterprise and open-source LLMs trained on text and
mathematical datasets on five symbolic tasks. The tasks occupy context-free and context-sensitive
categories on Chomsky’s hierarchy. We discussed the bit complexity of encoding symbolic tasks as an
automaton and set of knowledge tuples. Our experiments show that although enterprise LLMs perform
better than open-source models catering to higher parameters and curated dataset, all models show
similar trends in performance and align with knowledge-tuple encoding of symbolic tasks. Fine tuning
on these tasks as little efect on the performance of LLMs. This clearly shows that LLMs are not learning
the rules of symbol manipulation but rather encapsulate relationships in terms of tuples. The contrast
in the number of parameters required to encode symbolic tasks calls for a push in the direction of large
models capable of learning automaton rather than storing information.
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    </sec>
    <sec id="sec-7">
      <title>A. Chomsky’s Hierarchy</title>
      <p>
        Chomsky [
        <xref ref-type="bibr" rid="ref7">27</xref>
        ] [
        <xref ref-type="bibr" rid="ref8">28</xref>
        ] established a hierarchy (see Figure 7) delineating formal grammars according to their
complexity and the corresponding computational devices capable of recognizing languages generated
by these grammars. These grammars are classified from Type-3 to Type-0, with Type-0 representing
the highest level of complexity.
Definition A.1. A Deterministic Finite (State) Automaton is a 5-tuple, (, Σ, ,  0,  ), where  is
the set of all states, 0 ∈  is the initial state. Σ is the set of alphabets such that all input strings are a
subset of Σ* .  :  × Σ →  are a set of transition rules.  ⊆  are accepting states.
      </p>
      <p>A DFA reads input one symbol at time and updates its state determined by the transition rules  . The
input string is accepted if the DFA reaches a state  ∈  at the end of the input.</p>
      <p>Definition A.2. A Non-Deterministic Finite (State) Automaton is a 5-tuple similar to DFA with a
non-deterministic transition function  :  × (Σ ∪ { }) → (), where () is a power set of all
automaton states.</p>
      <p>All non-deterministic FSA can be reduced to their deterministic counterparts without the loss of
expressivity. Finite State Automata can accept all regular languages.</p>
      <p>Definition A.3. A Finite State Transducer (FST) is a finite state machine with an output tape. Formally
it is a 6-tuple, (, Σ, Γ, 0, ,  ) where Λ is the set of output alphabet, and  : ×{ Σ∪ } → ×{ Λ∪ }.
Definition A.4. A Pushdown Automaton is a 7-tuple, (, Σ, , ,  0, ,  ), where  is a set of stack
symbols and  ∈  is initial stack symbol. Transition function is defined as  : ×{ Σ∪ }×  → × *
Definition A.5. A Pushdown Transducer is a pushdown automata with an output tape. Specifically
it is a 8-tuple, (, Σ, Λ, , ,  0, ,  ), where Λ is a set of output symbols. All other symbols carry the
same meaning as a pushdown automata. The transition function is defined as  :  × { Σ ∪  } ×  →
 × { Λ ∪  } × *
Definition A.6. A Turing Machine is a 7-tuple, (, Γ, , Σ, ,  0,  ). Γ is the set of all tape alphabets.
 ∈ Γ is blank symbol, which is default on any on-empty cell on the tape. Input symbols are part of
tape symbols, Σ ⊆ Γ , and transition function is defined as  :  × Γ →  × Γ × { , , }. Here
{, , } are no shift, left shift and right shift of the tape pointer respectively.</p>
      <p>A FST can generate all regular languages and similarly, a pushdown transducer can generate all
context free languages. A linearly bounded automaton is a Turing Machine with a finite size tape.</p>
    </sec>
    <sec id="sec-8">
      <title>B. Symbolic Tasks and State Machines</title>
      <p>The five symbolic tasks discussed in this paper—sum of sequences, modular arithmetic, decimal
arithmetic, multiplication, and symbolic counting—can be accomplished using three fundamental operations:
addition, multiplication, and counting. In this section we will discuss how machines categorized in
chomsky’s hierarchy can be used for these operations.</p>
      <sec id="sec-8-1">
        <title>B.1. Addition</title>
        <p>The addition of two -digit numbers can be carried out by a two-state finite state transducer (FST).
Figure 8a depicts a construction that reads the digits of the two numbers from left to right and outputs
the result one digit at a time, from the least significant to the most significant digit. To add a sequence
of numbers, we add a stack to FST of figure 8a and make it non-deterministic (figure 8b).
(a) A two-state FST (Finite State Transducer) can add (b) To add a sequence of numbers, the finite state
matwo numbers by reading the digits of each number chine depicted in Figure 8a is augmented with a
from right to left, performing addition one digit at a stack to store intermediate addition results. A
nontime. The two states represent whether we need to deterministc pushdown transducer is required to
add a carry to the sum or not. ensure that the results are popped from the stack in
the correct order.</p>
      </sec>
      <sec id="sec-8-2">
        <title>B.2. Multiplication</title>
        <p>The multiplication of two multi-digit numbers necessitates a tape for storing partial products. As
depicted in Figure 9, a linearly bounded automaton (LBA) eficiently performs this task. It can solve
the multiplication of two multi-digit numbers by first calculating partial products and then combining
them to yield the final product. The number of digits in the partial products and the final product is
constrained by the number of digits in the given numbers. Consequently, a bounded tape is suficient
for evaluating the product.
Counting the occurrences of a specific character in a string can be achieved using a counter machine. In
Chomsky’s hierarchy, counter machines are more complex than finite state machines but less complex
than pushdown automata. Figure 10 shows a construction of a counter machine that can keep the
occurrences of a character in a given string. We also take help from a register to store the character to
match.</p>
      </sec>
    </sec>
    <sec id="sec-9">
      <title>C. Bit Encoding of a Number</title>
      <p>Proposition C.1. Given a number  in base , the model requires
to encode it in symbolic form.</p>
      <p>︀⌊ 1 + log( )⌋︀ · log2  bits
Proof. The number of digits  required to represent a number  in base  can be determined by the
formula:</p>
      <p>= ⌊︀ 1 + log( )⌋︀ .</p>
      <p>This expression arises because the largest number representable with  digits in base  is  − 1, and
thus:</p>
      <p>− 1 ≤  &lt; .</p>
      <sec id="sec-9-1">
        <title>Taking the logarithm base  of all parts of this inequality results in:</title>
        <p>− 1 ≤ log( ) &lt; .</p>
        <p>= ⌊︀ 1 + log( )⌋︀ .</p>
        <p>︀⌊ 1 + log( )⌋︀ · log2 .</p>
        <p>Adding 1 to each part and then taking the floor function provides the correct number of digits:</p>
        <p>Each digit in base  requires log2  bits for encoding since each digit can take any of  diferent
values, and log2  bits are suficient to uniquely identify each value. Therefore, the total number of bits
required to encode  is the product of the number of digits and the number of bits per digit:</p>
      </sec>
      <sec id="sec-9-2">
        <title>This completes the proof.</title>
      </sec>
    </sec>
    <sec id="sec-10">
      <title>D. Prompt Examples</title>
    </sec>
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