=Paper= {{Paper |id=Vol-3132/Paper_10 |storemode=property |title=On Parallel Processing of Machine Learning Based On Big Data and Voronoi Tessellation |pdfUrl=https://ceur-ws.org/Vol-3132/Paper_10.pdf |volume=Vol-3132 |authors=Vasyl Martsenyuk,Marcin Bernas,Aleksandra Klos-Witkowska,Tomasz Gancarczyk |dblpUrl=https://dblp.org/rec/conf/iti2/MartsenyukBKG21 }} ==On Parallel Processing of Machine Learning Based On Big Data and Voronoi Tessellation == https://ceur-ws.org/Vol-3132/Paper_10.pdf
On Parallel Processing of Machine Learning Based On Big Data
and Voronoi Tessellation
Vasyl Martsenyuk, Marcin Bernas, Aleksandra Klos-Witkowska and Tomasz Gancarczy
University of Bielsko-Biala, 2 Willowa, Bielsko-Biala, 43-309, Poland

                 Abstract
                 The paper is devoted to the development of an approach to machine learning for Big Data under
                 epistemic and aleatoric uncertainties which are taken into account with the help of
                 corresponding minimax criteria. The keystone of the method is processing subsets of training
                 data in parallel, using the partitioning based on Voronoi tessellation. Computational
                 complexity is analyzed and compared with sequential data processing. An example from a
                 medical application is considered, where the method is investigated for different learners and
                 resampling strategies.

                 Keywords 1
                 Parallel machine learning, Big Data, learner, uncertainty, minimax, Voronoi diagram

1. Introduction
    The active usage of Big Data technology in various branches [1-8] requires the development of high-
performance algorithm for solving the Machine Learning (ML) problems. To cope with Big Data
parallel computing is one of the most effective solution in the case of ML. It leads to the necessity of
the partitioning on Big Data sets. Voronoi diagrams are traditionally used for such type of problems.
    The minimax approach (together with maximin and maximax) is traditionally used for regression
problems [9], [10]. In the case of ML, one of the generalized minimax approaches is known as the
Minimax Probability Machine (MPM) [11].
    It can be argued that MPM is a classic result of studying the reliability of intelligent models [12],
[9], which can be considered as a typical method of classifying the reliability of learning. The task of
MPM optimization is to minimize the upper limit of the probability of incorrect classification of the
study of model parameters.
    The upper limit of the probability of incorrect classification can be used as an explicit indicator to
assess the reliability of classification models. A version of MPM with parametric reduction was
proposed in [11], [13] for nonlinear classification problems. Several advanced MPM algorithms have
been presented from different points of view [14], [15], [16], [17]. In [15], [16] it was pointed out that
in some cases it is necessary to distinguish the probability of incorrect classification of two classes, as
one class may be more important than another. In [18], MPM was extended for regression. In [9], MPM
was introduced to prepare the fuzzy classifier for a more transparent and understandable classification
model. In addition to MPM, the study of the reliability of intelligent models has been considered from
other points of view.
    For example, the concepts of "conflict" and "ignorance" were introduced to denote the reliability of
classification models in [19], [20].
    To make the method of adopting the minimum probabilistic method available for learning additional
intelligent models and to implement the study of the reliability of these models, a generalized hidden
minimum probability machine (GHM-MPM) is proposed. MPM classification was used as an explicit
indicator to characterize the reliability of the classification model.

Information Technology and Implementation (IT&I-2021), December 01โ€“03, 2021, Kyiv, Ukraine
EMAIL: vmartsenyuk@ath.bielsko.pl (A. 1); mbernaล›@ath.bieslko.pl (A. 2); awitkowska@ath. Bielsko.pl(A. 3); tgan@ath.bielsko.pl (A. 4)
ORCID: 0000-0001 -5622-1038(A. 1); 0000-0002-0099-1647 (A. 2); 0000-0003-2319-5974 (A. 3);0000-0002-9709-0860 (A. 4)
              ยฉ๏ธ 2022 Copyright for this paper by its authors.
              Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
              CEUR Workshop Proceedings (CEUR-WS.org)



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2. Description of the method
   The problem of supervised ML, which means the prediction of ๐›ถ with the help of ๐‘‹, loss function
๐ฟ, and the set of probability distributions ๐›ค on (๐‘‹, ๐‘Œ) can be formulated as minimax problem with the
respect to ๐ฟ, provided that the maximization is due to all possible distributions ๐บ and minimization is
with the respect to decision rules ๐œ“ โˆˆ ๐›น.
                                                      ๐‘Ž๐‘Ÿ๐‘” ๐‘š๐‘–๐‘› ๐‘š๐‘Ž๐‘ฅ๐›ฆ[๐ฟ(๐›ถ, ๐œ“(๐‘‹))]                                                          (2.1)
                                                             ๐œ“โˆˆ๐›น ๐‘ƒโˆˆ๐›ค

   where ๐ธ[โ€ข] is expectancy.
   The problem (2.1) can be solved with the help of introducing the generalization of the entropy
maximum principle. Mathematical description of the problem of supervised ML in systemic medical
research was presented in [21], [22]. Here we formulate it in the case of minimax criterion.
Mathematically ML problem for the systemic medical research is based on the following data. We have
dataset ๐ท, which includes ๐‘ tuples
                                                                ๏ป
                                                           D ๏€ฝ X i | i ๏€ฝ 1, N   ๏ฝ                                                       (2.2)
    In order to model aleatory uncertainties, consider supervised ML regarding the distribution of
learning tuples. For the class of all subsets of ๐ท we introduce ๐›ค, including the distributions of classes
of training and testing datasets

                          ๏‡ ๏€ฝ ๏ƒฌ๏ƒญ( Dtrain, j , Dtest, j ) ๏ƒŒ D ๏‚ด D | Dtrain, j ๏ƒ‡ Dtest, j ๏€ฝ ๏ƒ†, Dtrain, j ๏ƒˆ Dtest, j ๏€ฝ D, j ๏€ฝ 1,2 N ,๏ƒผ๏ƒฝ,   (2.3)
                               ๏ƒฎ                                                                                                   ๏ƒพ

   where Dtrain, j and Dtest, j are all possible datasets for training and testing correspondingly. In practice,
resampling strategies are distributions of the classes of tuples which are characterizing aleatoric
uncertainties the best. We introduce the resampling strategies ๐›พ โŠ‚ ๐›ค
                                 ๏ง ๏€ฝ ๏ป( Dtrain,k , Dtest,k ) ๏ƒŒ D ๏‚ด D | Dtrain, j ๏ƒ‡ Dtest, j ๏€ฝ ๏ƒ†,๏ƒˆk Dtrain,k ๏€ฝ ๏ƒˆk Dtest,k ๏€ฝ D๏ฝ,          (2.4)

    As examples of resampling strategies we can consider ๐‘๐‘ฃ3, ๐‘๐‘ฃ5, ๐‘๐‘ฃ10, which correspond to fold
cross-validation for different ๐‘˜.
    Each ๐‘– th tuple ๐‘‹๐‘– = (๐‘ฅ1๐‘– , ๐‘ฅ2๐‘– , . . . , ๐‘ฅ๐‘๐‘– , ๐›ถ ๐‘– )๐‘‡ consists of input data (๐‘ฅ1๐‘– , ๐‘ฅ2๐‘– , . . . , ๐‘ฅ๐‘๐‘– )๐‘‡ (called by also
attributes) and output data ๐›ถ ๐‘– .
    Let raw ๐‘ฅ๐‘— = (๐‘ฅ๐‘—1 , ๐‘ฅ๐‘—2 , . . . , ๐‘ฅ๐‘—๐‘ ) present the value of ๐‘— th attribute of all ๐‘ tuples. Output attribute ๐›ถ =
(๐›ถ , ๐›ถ 2 , . . . , ๐›ถ๐‘ ) includes all output data. The attributes ๐‘ฅ1 , . . . , ๐‘ฅ๐‘ and ๐›ถ (depending on the tasks of
   1

classification or regression) can accept both numerical and categorial values.
    In the simplest case, the supervised ML problem is to predict, using the certain predictor, the value
of output attribute ๐›ถ๐‘+1 based on the values of attributes ๐‘ฅ1 ๐‘+1 , . . . , ๐‘ฅ๐‘ ๐‘+1 . The predictor should
maximize the accuracy of prediction of output attribute, namely the probability
๐‘ƒ{๐›ถ ๐‘— ๐‘๐‘œ๐‘Ÿ๐‘Ÿ๐‘’๐‘ ๐‘๐‘œ๐‘›๐‘‘๐‘  ๐‘ก๐‘œ ๐‘ฅ1 ๐‘+1 , . . . , ๐‘ฅ๐‘ ๐‘+1 } for arbitrary ๐‘— โˆˆ {1, . . . , ๐‘}1 . Further, applying minimax
approach, we introduce โ„Ž โˆˆ ๐›น for the considered class of ML models โ„Ž(๐‘‹, ๐›พ), which can be trained and
tuned for the data ๐‘‹ โŠ‚ ๐ท and assessed taking into account certain resampling strategies ๐›พ. Comparing
different ML models, the goal is to minimize expected losses. But you also need to consider resampling
strategies, which should also assess the loss function. This formulation of the ML problem considers
two types of uncertainty. Namely, uncertainty in oversampling is aleatory because it is related to data.
At the same time, the uncertainty in the choice of models is epistemic. Mathematically, the minimum
problem of MN is described as a search for a model โ„Ž due to
                                                        ๐‘Ž๐‘Ÿ๐‘” ๐‘š๐‘–๐‘› ๐‘š๐‘Ž๐‘ฅ๐›ฆ[๐ฟ(๐›ถ, โ„Ž(๐‘‹, ๐›พ))]                                                     (2.5)
                                                                โ„Žโˆˆ๐›น ๐›พโˆˆ๐›ค


2.1.     The problem of the dimension reduction
   Because real sets of systemic medical studies include dozens of vital signs, morphological,
biochemical, and clinical assessments, it is natural to want to reduce the number of symptoms, leaving

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the ones with the greatest differences. The principal components analysis method (PCA) is one of the
widely used methods of dimensional reduction. Although it is used for unsupervised ML problems, it
helps us refine the results when used for supervised ML, such as a classification or regression problem.
The task of reducing the number of attributes is extremely important for medical use in interpreting the
results. Below we propose a method of its application in conditions of aleatory uncertainty.
    When regarding the Voronoi tessellation, the dimension reduction algorithm has to be applied for
each Voronoi cell. Moreover, since in the minimax ML (machine learning) problem the loss function
is calculated for all resampling strategies, the dimension reduction algorithm must be applied separately
                                                                                      ๐‘™
for each strategy ๐›พ. We can present arbitrary resampling strategy ๐›พ as ๐‘ˆ๐‘™๐‘Ÿ = ๐ผ๐‘ก๐‘Ÿ๐‘Ž๐‘–๐‘›๐‘–๐‘›๐‘”        (๐›พ), where
 ๐‘™
๐ผ๐‘ก๐‘Ÿ๐‘Ž๐‘–๐‘›๐‘–๐‘›๐‘” (๐›พ), ๐‘™ โˆˆ 1, ๐‘Ÿ is lth sample of indices from 1 to N, which corresponds to training tuples of the
strategy ๐›พ
                                                                  ๐‘™
    Let ๐ท๐‘™ (๐›พ) be input data coming from ๐ท, if sample of indices ๐ผ๐‘ก๐‘Ÿ๐‘Ž๐‘–๐‘›๐‘–๐‘›๐‘” (๐›พ) were applied. Namely,
              ๐‘– ๐‘–             ๐‘–    ๐‘– ๐‘‡
๐ท๐‘™ (๐›พ) = {(๐‘ฅ1 , ๐‘ฅ2 , . . . , ๐‘ฅ๐‘ , ๐›ถ ) } ๐‘™         , where Nl < N is the number of training tuples in
                                     ๐‘–โˆˆ{1...๐‘}โˆฉ๐ผ๐‘ก๐‘Ÿ๐‘Ž๐‘–๐‘›๐‘–๐‘›๐‘” (๐›พ)
the lth training sample.
   Before training and tuning the model โ„Ž(๐‘‹, ๐›พ), we reduce the dimension ๐‘ โˆˆ ๐‘ of D with the respect
to ๐›พ. For this purpose we offer the modification of PCA method with the respect to Voronoi cell and
resampling strategy ๐›พ (see Algorithm 1).
   Algorithm 1: PCA for the resampling strategy ๐›พ
                                                  ๐‘
   Input data: ๐ท = {(๐‘ฅ1๐‘– , ๐‘ฅ2๐‘– , . . . , ๐‘ฅ๐‘๐‘– , ๐›ถ ๐‘– )๐‘‡ }๐‘–=1 , ๐›พ
   Output: principle components together with the attributes.
        1 transform data D into the matrix A including all numerical entries;
                                                                                           ๐‘๐‘™
          2 apply resampling strategy ๐›พ for ะ: ๐ด๐‘™ = {(๐‘Ž1๐‘™,๐‘– , ๐‘Ž2๐‘™,๐‘– , . . . , ๐‘Ž๐‘๐‘™,๐‘– , ๐›ถ๐‘™,๐‘– )๐‘‡ }๐‘–=1 โˆˆ ๐‘…๐‘1 +1ร—๐‘๐‘™ , ๐‘™ = 1, ๐‘Ÿ;
      3      for each ๐ท๐‘™ (๐›พ), ๐‘™ = 1, ๐‘Ÿ do
                    1 ๐‘๐‘™
      4      ๐‘Ž๐‘™,๐‘– := โˆ‘๐‘—=1   ๐‘Ž๐‘–๐‘™,๐‘— , ๐‘– = 1, ๐‘1;
                    ๐‘๐‘™
      5      calculate ๐‘‰๐‘Ž๐‘Ÿ(๐‘Ž๐‘™,๐‘– ), ๐‘– = 1, ๐‘1;
                           ๐‘1
      6      ๐‘‰๐‘Ž๐‘Ÿ(๐ด๐‘™ ): = โˆ‘๐‘–=1   ๐‘‰๐‘Ž๐‘Ÿ(๐‘Ž๐‘™,๐‘– );
              โ€ฒ       ๐‘™,๐‘–
      7      ๐ด๐‘™ : = {๐‘Ž๐‘— โˆ’ ๐‘Ž๐‘™,๐‘– }๐‘–=1,๐‘1,๐‘—=1,๐‘๐‘™ โˆˆ ๐‘… ๐‘1ร—๐‘๐‘™ .;
                    1
      8      ๐ถ๐‘™ : = ๐‘ ๐ดโ€ฒ๐‘™ (๐ดโ€ฒ๐‘™ )๐‘‡ โˆˆ ๐‘… ๐‘1 .,
                     1
      9 calculate eigenvalues: ๐œ†๐‘™,1 โ‰ค ๐œ†๐‘™,2 โ‰ค. . . โ‰ค ๐œ†๐‘™,๐‘1
      10 calculate eigenvectors ๐ถ๐‘™ : ๐‘ค๐‘™,1 , ๐‘ค๐‘™,2 . . . ๐‘ค๐‘™,๐‘1               corresponding          to   ๐œ†๐‘™,1 โ‰ค ๐œ†๐‘™,2 โ‰ค. . . โ‰ค
         ๐œ†๐‘™,๐‘1 respectively
      11 ๐‘ƒ๐ถ1๐‘™ : = ๐ด๐‘‡๐‘™ ๐‘ค๐‘™,๐‘1 , ๐‘ƒ๐ถ2๐‘™ : = ๐ด๐‘‡๐‘™ ๐‘ค๐‘™,๐‘1โˆ’1 ;
        12 calculate variances ๐‘‰๐‘Ž๐‘Ÿ(๐‘ƒ๐ถ1๐‘™ ) ั‚ะฐ๐‘‰๐‘Ž๐‘Ÿ(๐‘ƒ๐ถ2๐‘™ );
                                              Var(PC1 )                                Var(PC2 )
           13 ExplainedVar(PC1๐‘™ ): = Var(๐ท )๐‘™ , ExplainedVar(PC2๐‘™ ): = Var(๐ท )๐‘™ ;
                                                      ๐‘™                                       ๐‘™
           14 ๐œ‹(๐‘ค๐‘™,๐‘1 ) ั‚ะฐ ๐œ‹(๐‘ค๐‘™,๐‘1โˆ’1 )
           End
                                       1
           16ExplainedVar(PC1๐‘™ ): = ๐‘Ÿ โˆ‘๐‘Ÿ๐‘™=1 ExplainedVar(PC1๐‘™ ),
                                                                    ๐‘Ÿ
                                                        1
                                  ExplainedVar(PC12 ): = โˆ‘ ExplainedVar(PC12 )
                                                        ๐‘Ÿ
                                                                  ๐‘™=1

      17 return names of attributes ะท ๐œ‹(๐‘ค๐‘™,๐‘1 ), ๐‘™ = 1, ๐‘Ÿั– ๐œ‹(๐‘ค๐‘™,๐‘1 โˆ’1 ), ๐‘™ = 1, ๐‘Ÿ
   Next, we describe the basic steps of Algorithm 1. In step 1, we convert all categorical attributes,
encoding them as a set of boolean inputs, each of which represents one category 0 or 1. We can generate
columns with category flags automatically.


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    Further we repeat the steps 4-14 for each ๐ท๐‘™ (๐›พ), ๐‘™ = 1, ๐‘Ÿ. So, they include the computing of mean
values of raws (Step 4), variance ๐‘‰๐‘Ž๐‘Ÿ(๐‘Ž๐‘™,๐‘– ), ๐‘– = 1, ๐‘1 (Step 5), general variance (sum of sample
variances) ๐‘‰๐‘Ž๐‘Ÿ(๐ด๐‘™ ) (Step 6), deviation matrix ๐ดโ€ฒ๐‘™ โˆˆ ๐‘… ๐‘1ร—๐‘๐‘™ (Step 7), covariance matrix ๐ถ๐‘™ โˆˆ ๐‘… ๐‘1 (Step
8), eigenvalues of matrix ๐ถ๐‘™ due to increasing order (Step 9), eigenvectors ๐ถ๐‘™ (Step 10). Here we
consider eigenvectors ๐‘ค๐‘™,๐‘1 and ๐‘ค๐‘™,๐‘1โˆ’1 โˆˆ ๐‘… ๐‘1 , which correspond to ๐œ†๐‘™,๐‘1 and ๐œ†๐‘™,๐‘1โˆ’1 respectively. At
the step 11 we get two principle components ๐‘ƒ๐ถ1๐‘™ : = ๐ด๐‘‡๐‘™ ๐‘ค๐‘™,๐‘1 and ๐‘ƒ๐ถ2๐‘™ : = ๐ด๐‘‡๐‘™ ๐‘ค๐‘™,๐‘1 โˆ’1 . We calculate
their variances Var (PC1l) and Var (PC2l) at step 12. From this we obtain the percentages of the
explained variance corresponding to the first two components ExplainedVar (PC1l) and ExplainedVar
(PC2l) respectively (Step 13). Next, we organize the values of the eigenvectors ๐‘ค๐‘™,๐‘1 ั– ๐‘ค๐‘™,๐‘1โˆ’1 in
descending order of their absolute values. For this purpose, we use permutations ๐œ‹(๐‘ค๐‘™,๐‘1 ) and
๐œ‹(๐‘ค๐‘™,๐‘1 โˆ’1 ). We use the denotion ๐œ‹(๐‘ฅ) for a permutation that organizes the vector x in descending order
of the absolute values of its elements.
    Next we return the names of the first ExplainedVar (PC1l) 100% attributes in permutation ๐œ‹(๐‘ค๐‘™,๐‘1 )
and the first ExplainedVar (PC2l) 100% attributes in permutation ๐œ‹(๐‘ค๐‘™,๐‘1 โˆ’1 ) (Step 14).
    After completing the main cycle, we calculate the variance of the main components for the
resampling strategy \ gamma (Step 16). Finally, we return the names of the first ExplainedVar (PC1l)
100% attributes, which are most common in permutations ๐œ‹(๐‘ค๐‘™,๐‘1 ), ๐‘™ = 1, ๐‘Ÿ and the first ExplainedVar
(PC2l) 100% attributes that are most common in permutations ๐œ‹(๐‘ค๐‘™,๐‘1 โˆ’1 ), ๐‘™ = 1, ๐‘Ÿ (Step 17).
   As a result of reduction of dimension we receive some numerical matrix ๐ด๐‘Ÿ๐‘’๐‘‘ =
                          ๐‘
{(๐‘Ž1๐‘– ; ๐‘Ž2๐‘– , . . . , ๐‘Ž๐‘๐‘– 2 , ๐›ถ ๐‘– )๐‘‡ }     โˆˆ ๐‘…๐‘2 +1ร—๐‘ , ๐‘2 โ‰ค ๐‘1. These data can then be used as training to solve ML
                                       ๐‘–=1
problems based on the minimax approach.
    Note 1. Stages 2 and 10-14 are modifications of the traditional PCA algorithm. First, in step 1, we
convert all categorical attributes that are widely used in systemic medical research into boolean data.
Second, when considering the two main components traditionally used for planar presentation of
training kits, we propose an approach to selecting some reduced number of attributes for further research
(e.g., developing a ML model). This number is related to the number of variations explained. The latter
assumption allows us to truly reduce the size of ML problems in systemic medical research under
uncertainty.
    Note 2. Of course, we must take into account the case if the variance due to the first two components
is low. In such cases, we need to take into account the components PC3, PC4 and so on to obtain the
appropriate dispersion. Steps 10-14 and other algorithms should be changed accordingly.
    Note 3. It should be noted that the PCA should be calculated depending on the resampling strategy,
as the PCA is applied to training tuples. ๐ท๐‘™ (๐›พ) (not for the whole data set D). Therefore, in Step 14,
                                                                                      ๐‘™
different features may be selected depending on the sample of indices ๐ผ๐‘ก๐‘Ÿ๐‘Ž๐‘–๐‘›๐‘–๐‘›๐‘”              (๐›พ). In turn, this affects
the selection of attributes in the last step of the algorithm for the entire resampling strategy.

2.2. General flowchart of parallel machine learning with the help of Voronoi
diagrams
   The general block diagram (Figure 2.1) allows us to obtain a learner of the ML problem based on a
minimax approach with the possibility of accurate, acceptable and stable results. The MN model,
formulated under conditions of certainty, is presented in [22]. Here, we summarize a flowchart for
solving the problem under uncertainty in both the model and the resampling strategy.
   We start with the import and preparation of data (feature generation, gap filling, normalization)
collected in EMR systems. Methods of importing data sets from EMR systems are presented. Note that
the choice of open source EMR systems over commercial ones is extremely important because it allows
open access to clinical data that can be processed and selected for subsequent stages of ML [22].
   Then we should define the task from the point of view of MN. This can be regression, classification,
grouping, and so on. Resampling strategies ๏ง are also defined. For example, resampling strategies

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supported by the mlr package include: cross-validation (cv), cross-validation (LOO), re-cross-
validation (RepCV), color subsampling, also called Monte Carlo cross-validation (Subsample), Holdout
method (training / testing) (Holdout) [23]. In a real application, we are dealing with a large number of
attributes. Only some of them can be important for the tasks of MN. Therefore, it is natural to try to
reduce the dimension by discarding the attributes with the largest deviations.
    Next we specify the set ัฐ of appropriate methods (learner) of the solution. The most important is
the choice of parameters for the methods, which affects the accuracy of the model. In the next cycle,
configure the parameters for each model with ัฐ based on all resampling strategies ๏ง , which are used.
The original model will satisfy the criterion of the minimax approach (2).


                                                        Minimax
                                                        ML model


                                                                           Minimization of โ„Ž โˆˆ ฮจ
                                          Result voting for
                                          Voronoi cells


  Prepar        Determ         Voronoi    Resam           Choos                                      Assessment
   ation         ining                     pling           ing           Dimension         Tuning
                               tesselat                                                                 of loss
    of            task                    strateg         model          reduction         model
                                 ion                                                                   function
   data                                     ies            โ„Ž โˆˆ                             โ„Ž(๐‘‹, ฮณ)
                                                                                                     ๐ฟ(๐‘Œ, โ„Ž(๐‘‹, ฮณ))
                                          ๐›พโˆˆ ฮ“              ฮจ



              Regression,
                                                                Maximization of ๐›พ โˆˆ ฮ“
             classification,
              grouping, ...


Figure 2.1: Development of a parallel ML model for systematic medical research
   The capabilities of the mlr package allow us to implement this using appropriate tools designed with
certain tasks in mind [24], [25], [26]. The ML model presented above is fully consistent with the mlr
package, which offers prototypes of the ML problem cases: task, resampling, learning.

2.3.       Computational complexity
   In order to analyze the computational complexity of the proposed approach, consider an example of
a set ัฐ, which includes the method of a 4-layer neural network with the number of neurons ๐‘–, ๐‘—, ๐‘˜, ๐‘™ on
layers based on inverse error propagation and method C5.0 induction of decision tree height โ„Ž.
   Assume that the training data sample ๐ท includes #(๐ท) tuples based on ๐‘– attributes.
   Let ๐‘ฃ be the number of seeds for Voronoi tessellation. Corresponding computational complexity is
                                                                           ๐‘–
                                          ๐‘‚๐‘‰๐ท โ‰” ๐‘‚ (๐‘ฃ ๐‘™๐‘œ๐‘” ๐‘ฃ + ๐‘ฃ โŒˆ2โŒ‰ )

  The computational complexity of the specified neural network method based on ๐‘ก iterations is
Error! Reference source not found.:
                                     ๐‘‚๐‘๐‘ : = ๐‘‚(๐‘ก#(๐ท)(๐‘–๐‘— + ๐‘—๐‘˜ + ๐‘˜๐‘™))                       (2.6)

   Computational complexity of decision tree induction [28]:
                                                    ๐‘‚๐ถ5.0 โ‰” ๐‘‚(โ„Ž#(๐ท) ๐‘™๐‘œ๐‘” #( ๐ท))                                       (2.7)
   Computational complexity of resampling based on ๐‘˜-fold cross validation is Error! Reference
source not found.:
                                                              ๐‘‚๐ถ๐‘‰ = ๐‘‚(๐‘˜#(๐ท))                                         (2.8)


                                                                                                                      108
   Thus, the computational complexity of constructing the ML model based on the scheme in Figure
2.1 is
                                   ๐‘‚๐‘€๐ฟ = ๐‘‚๐‘‰๐ท ๐‘‚๐ถ๐‘‰ (๐‘‚๐‘๐‘ + ๐‘‚๐ถ5.0 )                             (2.9)
   Since k is constant, then from (2.9) shows that the computational complexity increases by one order
of magnitude.

3. Example of the medical data
    Modern systemic medical research (evidence-based medicine) is the integration of the best scientific
evidence with clinical experience and patient expectations [30]. They are aimed at improving health
care in the future. Systematic medical research helps doctors and researchers gain knowledge about
human health and disease. They also allow you to find more effective ways to prevent and treat disease.
Assessment of health is based on a comprehensive and systematic examination of the patient, which
includes history, objective examination of the body, analysis of laboratory blood tests and various
secretions, instrumental and interventional studies, including X-ray, CT, MRI, endoscopy, biopsy and
others methods.
    Nowadays, cardiovascular diseases attract attention because they are "the number one cause of death
in the world" [31]. In the study of cardiac diseases, there are quite a number of nuances and indicators
that experts pay attention to during diagnosis. Diagnostic criteria include both physical tests and history,
as well as laboratory, instrumental research methods. During the survey, the doctor may ask questions
about the patient's family members (genetic predisposition), lifestyle and habits. Physical inactivity
(sedentary lifestyle), unhealthy diet, alcohol consumption and smoking significantly increase the risk
of cardiovascular disease. During laboratory studies, much attention is paid to the assessment of the
level of lipids and their fractions (lipid profile). It includes indicators of total cholesterol, triglycerides,
high, low, very high and very low lipoprotein density, as well as the level of atherogenicity. Lipid
imbalance increases the risk of atherosclerosis. Among other things, the patient's overweight is one of
the dangerous risk factors for heart disease. Blood glucose and glycated hemoglobin are among the
most important indicators of carbohydrate metabolism in the body and markers of diabetes. Diabetes is
a separate disease, but its presence significantly increases the risk of cardiovascular disease. In addition
to the risk assessment, the necessary extended hematological, biochemical and instrumental studies are
performed. In addition to the general blood test, the patient's blood pressure is measured, the following
instrumental methods are used: electrocardiogram (ECG), Holter monitoring, echocardiography,
coronary angiography, MR angiography.
    This experimental study includes data from 1651 patients diagnosed with myocardial infarction. The
target attribute of forecasting is life expectancy. Each patient's data includes 97 attributes that contain
both numerical and categorical values. Such information includes data on the type of heart attack (focal
or transmural), the location of the heart attack (anterior or posterior). Mortality information (hospital,
short-term and long-term) is also used. The presence of concomitant pathologies is described. And here
we use a detailed analysis, because such pathologies can be combined. Risk factors typical of
cardiovascular diseases are investigated, namely, clinical evaluation includes data on such risk factors
as gastritis, gallstone disease, lung disease, nephrological disorders, rheumatic thyroid disease,
angiopathology, gastrointestinal diseases, oncology, chronic obstructive pulmonary disease,
hypertension, diabetes, smoking.
    The considered detailed clinical course includes indicators of vital functions, namely heart rate,
systolic blood pressure and diastolic blood pressure, analyzes of heart attack complications in the form
of arrhythmias, in particular, detailed heart attack complications developed in the hospital. The data
lists all indicators of the general analysis of blood. Special attention is paid to leukocytes (WBC),
biochemical analysis of blood is presented, information on medicines which the patient received in
hospital is included. After the dimension reduction algorithm, the following features remained: sex,
age, re-myocardial infarction (RMI), life expectancy after MI (death_days), body mass index (BMI),
leukocyte density (White_blood_cells_count), left ejection fraction ventricle (LVEF).


                                                                                                           109
    We consider set ัฐ, which includes the models of linear regression (regr.lm), SVM model with radial
base kernel (regr.ksvm), and random forest (regr.ranger).
    Resampling strategies include cross-validation of cv3, cv5, cv7, cv9, cv10. The loss function L was
calculated as the rmsse rmse and the training time. In the case of RMSE as an indicator of efficiency
(Table 2.1), the regr.ksvm model is a solution of the ML problem based on the minimax. Namely, we
first compare the error values for all the models considered. In the second step, we see that the RMSE
value for the ksvm model will be minimal among the maximum. In Figure 2.2 we can see the analysis
of the effectiveness of ML models with different resampling strategies for standard deviation as an
indicator of efficiency.




Figure 2.2: Comparison of the effectiveness of ML models for different resampling strategies (cv3, cv5,
cv7, cv9, cv10) based on RMSE
Table 2.1.
RMSE of ML model
        Resampling            Linear regression                SVM                 Random forest
        strategy
            cv3                 0.2100193167              0.03786423738            0.04423246658
            cv5                  0.210649921              0.02506639264            0.02696577121
            cv7                 0.2106224629              0.02404772839            0.02362994412
            cv9                 0.2098297672              0.02371189948            0.01803804644
           cv10                 0.2102195218              0.02263394791            0.0164288483
            max                  0.210649921              0.03786423738            0.04423246658
          minimax                                         0.03786423738



                                                                                                   110
Table 2.2.
Training time of ML model
         Resampling            Linear regression               SVM                 Random forest
        strategies
             cv3                  0.006666667               6.05333333               15.62000000
             cv5                   0.0020000               13.98800000               35.35600000
             cv7                   0.0000000               18.52428571               45.66714286
             cv9                  0.002222222               25.152222                65.76222222
            cv10                   0.0050000               28.64400000               76.46600000
             max                  0.006666667              28.64400000               76.46600000
           minimax                0.006666667




Figure 2.3: Comparison of the effectiveness of ML models for different resampling strategies (cv3, cv5,
cv7, cv9, cv10) based on training time.

4. Conclusions
    Based on the above examples, it is established that taking into account the uncertainty in the data
(aleatory uncertainty) significantly affects the model based on ML.

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   For example, as can be seen from Table 2.2, there is a resampling strategy (namely cv10), in which
the random forest model shows the lowest value of the RMSE loss function on the set of all models
considered.
   At the same time, there are resampling strategies (cv3), in which this model shows greater errors
compared to the model of SVM. In this situation, the choice of a random forest model would lead to
unexpected losses arising from aleatory uncertainty.
   Therefore, the minimax approach proposes to establish a resampling strategy with the maximum
("worst") value of the loss function, on which the desired model should behave best (get the minimum
value of the loss function).

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