<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.0 20120330//EN" "JATS-archivearticle1.dtd">
<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>Kyiv, Ukraine, June</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>Calculation Methods of the Prognostication of the Computer Systems State under Different Level of Information Uncertainty</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Igor P. Atamanyuk</string-name>
          <email>atamanyuk_igor@mail.ru</email>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Yuriy P. Kondratenko</string-name>
          <email>y.kondratenko@csuohio.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vyacheslav S. Shebanin</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Cleveland State University</institution>
          ,
          <addr-line>2121 Euclid Av., 44115, Cleveland, Ohio</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Mykolaiv National Agrarian University, Commune of Paris str.</institution>
          <addr-line>9, 54010 Mykolaiv</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Petro Mohyla Black Sea State University</institution>
          ,
          <addr-line>68th Desantnykiv Str. 10, 54003 Mykolaiv</addr-line>
          ,
          <country country="UA">Ukraine</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2016</year>
      </pub-date>
      <volume>2</volume>
      <fpage>1</fpage>
      <lpage>24</lpage>
      <abstract>
        <p>Calculation methods of the prognostication of the computer systems state under different volume of a priori information and accuracy of the measurement of controlled parameters (under absence and presence of measurement errors) are obtained in the work. Canonical expansions of random sequences of the indices characterizing the state of the investigated systems considered as basic features of the methods. Synthesized methods do not impose any significant limitations on the qualities of the sequence of the change of the forecast parameters (linearity, stationarity, Markov behavior, monotoneness, etc.) and allow to take into account the stochastic peculiarities of the process of functioning of the investigated objects as much as possible. Expressions of the determination of a mean-square extrapolation error are obtained for solving the prognostication problems specifically concerning the state of computer systems under different level of information uncertainty.</p>
      </abstract>
      <kwd-group>
        <kwd />
        <kwd>calculation method</kwd>
        <kwd>random sequence</kwd>
        <kwd>canonical decomposition</kwd>
        <kwd>prognostication of the state</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>-</title>
      <p>- 293
1 Mathematical statement of the problem of the prognostication of
a technical condition
One of the most important problems that arises constantly in the process of the
operation of computer systems and computerized control systems [1,2,3] is based on quite
evident fact that any decision about the permission of the system operation (of the
realization of a stated problem) is closely connected with the solving of the prognosis
problem. For example, the forecast of the remaining functioning time is a rotating
machinery prognosis, results of which can be used also for forecasting of the
reliability of machinery components (and additional equipment) as well as for forecasting
future operational conditions. This kind of prognosis is based on the output data of
multi-sensor monitoring system and current results of data processing. The main goal
of such prognosis deals with: (a) reducing downtime of the machinery and
corresponding equipment; (b) optimizing spares quantity; (c) decreasing functioning cost;
(d) increasing safety of the machinery maintenance. In [4] authors analysis known
methods of rotating machinery prognosis and classify the approaches to three groups
based on different models: (a) general reliability, (b) environmental conditions, (c)
combining prognostication and reliability.</p>
      <p>Special attention should be paid to prognostication of manufacturing and industrial
systems [5]. The results of such prognosis can help to determine the most rational
maintenance modes for long-time functioning of different computer-integrated
technological complexes. Modelling the degradation mechanism and dynamical
degradation monitoring of the most important components of computer-integrated
technological complexes are the base for prognosis in [5] within an e-maintenance architecture.</p>
      <p>Different forecasting methods can be used for short-term electric load prognosis
[6,7] at the enterprises, plants, cities and regions. The surveys of the prognosis
methods based on applying Kalman filter, state space models, linear regression, stochastic
time series, various smoothing algorithms, and artificial intelligence methods as well
as the analysis of their application for solving prognostication problems is presented
in [6,7] with implementation to short-term electric load prognosis.</p>
      <p>The uncertainties of functioning conditions, external environment, nonstationary
parameters and working modes and problems with their mathematical formalization
are the main obstacles in using efficient computer models for forecasting future
behavior of complex technological systems. As example, in [8] authors consider a
special Bayesian computer model for prognostication of the active hydrocarbon reservoir
future functioning.</p>
      <p>Last years, such powerful theoretical-applied tool as the theory of neuro-fuzzy
systems has been introduced successfully for solving different prognostication tasks in
engineering, medicine, investment policy, finance and other fields [9,10,11,12,13].</p>
      <p>According to reliability of control systems, it is necessary to note that computers
are the main components of embedded controllers (traditional, fuzzy, neuro, etc.). The
main critical requirement deals with providing efficient functioning such systems and
networks in normal and in failure modes, when any component fails. One of the
efficient approach for design process of such control systems is based on the applying
redundant-elements-design-method [14].</p>
      <p>Two most important indexes can be taken in to account in solving forecasting tasks
for the e-business systems: (a) insufficient speed of response and (b) preventing
failure of the system. In [15] author consider predictive inputs for the designed prognosis
system as intrinsic (component activity levels, system response time, etc.) and
extrinsic (time, date, whether, etc.) variables.</p>
      <p>The prognostication in computer networks is described in [16] for forecasting the
level of computer virus spread based on two models of viral epidemiology
(differential equation model and the discrete Markov model).</p>
      <p>The problem of forecasting control is especially topical for computer systems
which are used for the management of the objects that relate to the class of critical or
dangerous and under the threat of accident objects (aircraft, sea mobile objects,
nuclear power stations, chemical industry plants etc.) [17,18,19].</p>
      <p>Computer systems are exploited in the conditions of continuous influence on the
great number of external and internal perturbing factors, the influence on the object of
which is random by the moment of origin, duration and intensity. And
correspondingly the changes of the system state also turn out to be random and form a random
sequence. Thereupon the extrapolation of the realization of the random sequence
describing the functioning of the investigated system on a certain interval of time is the
mathematical content of the problem of the prognostication of a technical condition.</p>
      <p>The most general extrapolation form for the solving of the problem of non-linear
extrapolation is a Kolmogorov-Gabor polynomial [20] but it is very difficult and
laborious procedure to find its parameters for the great number of known values and used
order of non-linear relation. Thereupon during the forming of realizable in practice
algorithms of the prognosis different simplifications and restrictions on the qualities
of random sequence are used. For example, a range of suboptimal methods of
nonlinear extrapolation with a limited order of stochastic relation on the basis of
approximation of a posteriori density of probabilities of an estimable vector by an
orthogonal expansion by Hermite polynomials or in the form of Edgeworth series
was offered by V.S. Pugachev [21]. Solution of non-stationary equation of A.N.
Kolmogorov [20] (particular case of differential equation of R. L. Startanovich for the
description of Markovian process) is obtained provided that the drift coefficient is
linear function of state and coefficient of diffusion is equal to constant. Exhaustive
solution of the problem of optimal linear extrapolation for different classes of random
sequences and different level of informational support of the problem of prognosis
(A.N. Kolmogorov equation [22] for stationary random sequences measured without
errors; Kalman method [23] for markovian noisy random sequences; Wiener-Hopf
filter-extrapolator [24] for noisy stationary sequences; algorithms of optimal linear
extrapolation of V. D. Kudritsky [25] on the basis of canonical expansion of V. S.
Pugachev etc.) exists. But maximal accuracy of the prognosis with the help of the
methods of linear extrapolation can be achieved only for Gaussian random sequences.</p>
      <p>Thus the development of the new methods of the prognostication of computer
systems state which allow to take into account the information about the investigated
object as much as possible is a topical problem.</p>
      <p>Let us assume without restricting the generality that the state of a computer system
is determined in exhaustive way by scalar parameter X the change of the values of
which in discrete range of points ti , i  1, I is described by the discrete sequence
{X }  X (i), i  1, I . It is necessary to get optimal estimations of future values of a
random sequence under different volume of a priori and a posteriori information.
2 Prognostication under the absence of the errors of measurement
The most universal from the point of view of the limitations that are imposed on the
investigated sequence is the method on the basis of canonical model [26]:
i N
X i   M  X i    W( )1( ) i  , i  1, I ,</p>
      <p> 1  1
where elements W ( ) ,  h( ) i  are determined by recurrent correlations:
</p>
      <p> 1 N  1
W( )  X     M  X      W( j)(j)    W( j)(j)   ,   1, I ;
 1 j1 j1
 h( ) i  </p>
      <p>M W( )  X h i   M  X h i  </p>
      <p>M W( ) 2 
 
</p>
      <p>1
D  </p>
      <p>{M  X    X h i  
 1 N
M  X    M  X h i     Dj   (j)    h(j) i  </p>
      <p> 1 j1
 1
 Dj   (j)    h(j) i },   1, h,   1, i, h  1, N , i  1, I.</p>
      <p>j1
D    M W( ) 2   M  X 2    M 2  X    </p>
      <p> 
1 N D j  (j)  2  1 D j  (j)  2 ,  =1, N ,  1, I ;</p>
      <p> 1 j1 j1</p>
      <p>
        The method of extrapolation on the basis of mathematical model (
        <xref ref-type="bibr" rid="ref1">1</xref>
        ) has two forms
of notation [27,28,29]
 M  X h i  when   0;


m( ,l)  h, i    m( ,l 1)  h, i    xl    m( ,l1) l,    h(l) i  when l  1,
x x x

mx( 1,N )  h, i    xl    m( 1,N ) l,    h(1) i  when l  1.
      </p>
      <p>
        x
(
        <xref ref-type="bibr" rid="ref1">1</xref>
        )
(
        <xref ref-type="bibr" rid="ref2">2</xref>
        )
(
        <xref ref-type="bibr" rid="ref3">3</xref>
        )
(
        <xref ref-type="bibr" rid="ref4">4</xref>
        )
(
        <xref ref-type="bibr" rid="ref5">5</xref>
        )
x i  , i  k 1, I provided that for the calculation of the given estimation values
x  j  ,   1, N , j  1, k are used that is the results of the measurements of sequence
X  in points t j , j  1, k are known.
3 Prognostication on the basis of a priori information about the
sequence of measurements with errors
Solution of the problem of prognosis (
        <xref ref-type="bibr" rid="ref5">5</xref>
        ),(
        <xref ref-type="bibr" rid="ref6">6</xref>
        ) presupposes the usage of true values of
random sequence X  in the points of discretization t j , j  1, k . But in real situations
the assumption about that that measured values x  j  , j  1, k are known absolutely
exactly is never carried out. The errors of the determination of the values of the
forecast parameter can appear whether as a result of overlay of hindrances in the
communication channel between measuring device and investigated object or as a result of
influence of hindrances on the measuring tools.
      </p>
      <p>
        Let us assume that as a result of measurements random sequence is observed
(
        <xref ref-type="bibr" rid="ref6">6</xref>
        )
(
        <xref ref-type="bibr" rid="ref7">7</xref>
        )
(
        <xref ref-type="bibr" rid="ref8">8</xref>
        )
(
        <xref ref-type="bibr" rid="ref9">9</xref>
        )
where Y (i), i  1, I , is a random error of measurement, X (i), i  1, I , is unobserved
component. It is necessary to obtain optimal (in mean-square sense) estimation of
future values of random sequence  X  : M  X  ( ) X h i  , , h  1, N , , i  1, I by
the results of measurements z  j  , j  1, k.
      </p>
      <p>
        Within the limits of such a statement the simplest nonoptimal solution of the
problem presupposes the usage of algorithms (
        <xref ref-type="bibr" rid="ref5">5</xref>
        ),(
        <xref ref-type="bibr" rid="ref6">6</xref>
        ) substituting in it the results of
measurements
 M  X h i  ,   0;


mx(/z,l)  h, i    mx(/z,l 1)  h, i    zl ( )  mx(/z,l 1) l,    h(l) i  , l  1;

mx(/z1,N )  h, i    zl ( )  mx(/z1,N ) l,    h(1) i  , l  1;
      </p>
      <p>k N
mx(k/ z,N ) 1, i   M  X i      z  j   M Z  j   S(((kjN)1)N  ) i 1 N  1.</p>
      <p>j1  1</p>
      <p>Conditional mathematical expectation remains as before unbiased estimation of
future values of true extrapolated realization. At the same time the error of a single
extrapolation will be written down as:</p>
      <p>(xk/z) i   mx(k/ z) 1, i   x(k ) i  , i  k  1, I ,
where x(k ) (i), i  k  1, I is a true value of extrapolated realization in the area of
forecast. These values aren’t known actually and realization x(k ) i  is developing in a
random way in the area of forecast. As a result of this the error of a single
extrapolation acquires random character:
Sx(k/z) i / z  j  ,   1, N , j  1, k   mx(k/ z,N ) 1, i   m(k ,N ) 1, i  </p>
      <p> x
k N
    z  j   M Z  j   S(((kjN)1)N  ) i 1 N 1 </p>
      <p>j1 1
The application of the operation of mathematical expectation to the last expression
shows that in the given case (as distinct from an ideal case) a single extrapolation is
accompanied by conditional systematic error.</p>
      <p>
        Correspondingly the dispersion of the error of a single extrapolation from (
        <xref ref-type="bibr" rid="ref13">13</xref>
        ),
(
        <xref ref-type="bibr" rid="ref14">14</xref>
        ) is determined as
      </p>
      <p>M  x(/kz) i   Sx(k/z) i 2   jik 1N11 D  j 1(j ) i 2 , i  k  1, I.</p>
      <p>
        With the usage of (
        <xref ref-type="bibr" rid="ref13">13</xref>
        ), (
        <xref ref-type="bibr" rid="ref14">14</xref>
        ) mean-square error of a single extrapolation will be
written down in the form
      </p>
      <p>Ex(/kz) i / z   ,   1, k   Sx(k/z) i 2  D(k ) i  , i  k  1, I.</p>
      <p>
        x
As error (
        <xref ref-type="bibr" rid="ref16">16</xref>
        ) is conditional averaging (
        <xref ref-type="bibr" rid="ref16">16</xref>
        ) by condition that values z   ,   1, k
are random is necessary for complete characteristic of the accuracy of algorithm (
        <xref ref-type="bibr" rid="ref11">11</xref>
        ),
(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ). As a result the expression for mean-square error of prognosis is in the form
k N k N
Ex(k/z) (i)  Dx(k/z,N ) i       M Y  l Y  j  S(((klN1))N  ) i 1 N  1 
l1  1 j1  1
S(((kjN)1)N  ) i 1 N  1  i N1 D  j 1(j ) i 2 , i  k  1, I.
      </p>
      <p>jk 1 1</p>
    </sec>
    <sec id="sec-2">
      <title>4 Prognostication measurements with preliminary filtration of the errors of</title>
      <p>Increase of the quality of extrapolation of random sequence  X  , measured with
noises is possible at the expense of transition from the results of measurement
z   ,   1, k, k  I to estimation.</p>
      <p>x*    M  X    1  F ( )  m(* 1,N ) 1,    F ( ) zo   ,   1, k.</p>
      <p>
        x
(
        <xref ref-type="bibr" rid="ref15">15</xref>
        )
(
        <xref ref-type="bibr" rid="ref16">16</xref>
        )
(
        <xref ref-type="bibr" rid="ref17">17</xref>
        )
      </p>
      <p>Unbiased estimation of unknown value x   being studied as a balanced mean
value of the result of the forecast at  -th step m(*k,N 1) 1,   and result  - of that
x
measurement z( ) .</p>
      <p>
        By means of consecutive substitution with the application of estimation (
        <xref ref-type="bibr" rid="ref18">18</xref>
        ) the
algorithm of extrapolation (
        <xref ref-type="bibr" rid="ref5">5</xref>
        ) is brought to the form [30]:
 M  X h (i) ,   0;


m(* ,l)  h, i    m(* ,l1)  h, i   F ( )  zl ( )  m(* ,l 1) l,    h(l) i  , l  1;
x  x x
m(* 1,N )  h, i   F ( )  zl ( )  m(* 1,N ) l,    h(1) i  , l  1.
      </p>
      <p>
         x x
Algorithm (
        <xref ref-type="bibr" rid="ref19">19</xref>
        ) has equivalent form of notation as following
mx(*k,N ) 1, i   M  X i   jk1 N1  zo  j   G(((kjN)1)N  ) i 1 N  1 ,
      </p>
      <p>G( 1)    G( 1)   k i  ,    -1;
G( )     
     ,  = ;
F ([ / N ]1) (modN1 ( ))  / N   1 , for   kN ;
 1,[ / N ]1
     </p>
      <p>F ([ / N ]1)1(,m[o/dNN ](1)) i  , if  = i -1 N  1.</p>
      <p>Optimal values of weight coefficients are determined from the condition of
minimum of mean-square error of filtration</p>
      <p>E f  k   M  X *  k   X  k  2   M  1  F (k )  jk1 N1  Zo  j   
o 2 
G((kjN1))(N  )  k 1 N  1  F (k ) Zo  k   X  k   .

</p>
      <p>After differentiation of this expression on F (k ) and solution of the corresponding
equation the expression for calculation of the optimal value of the coefficient is
obtained</p>
      <p>F (k ) </p>
      <p>
        F (k )  F (k )  F (k )
1 2 3
F (k )  F (k )  2F3(k )  Dy  k 
1 2
(
        <xref ref-type="bibr" rid="ref19">19</xref>
        )
(
        <xref ref-type="bibr" rid="ref20">20</xref>
        )
(
        <xref ref-type="bibr" rid="ref21">21</xref>
        )
(
        <xref ref-type="bibr" rid="ref22">22</xref>
        )
(
        <xref ref-type="bibr" rid="ref23">23</xref>
        )
(
        <xref ref-type="bibr" rid="ref24">24</xref>
        )
past measurements and summand Dy  k  is dispersion of the last measurement.
Algorithm (
        <xref ref-type="bibr" rid="ref19">19</xref>
        ),(
        <xref ref-type="bibr" rid="ref20">20</xref>
        ) got on the basis of function M  X  ( ) X h i  , , h  1, N , , i  1, I
and results of measurements z( j), j  1, k provides minimum of mean-square error of
the prognosis for the given volume of known information about investigated random
sequence as two interconnected consecutive stages (filtration-extrapolation) are
fulfilled in optimal way: weight coefficients of estimation (
        <xref ref-type="bibr" rid="ref18">18</xref>
        ) are determined from the
condition of the minimum of mean-square error of approximation to true values and
parameters of extrapolator on the stage of preliminary filtration and further forecast
are optimal which was proved earlier in the theorem.
      </p>
      <p>
        Mean-square error of extrapolation with the use of the algorithm of polynomial
filtration (
        <xref ref-type="bibr" rid="ref19">19</xref>
        ),(
        <xref ref-type="bibr" rid="ref20">20</xref>
        ) is determined as
      </p>
      <p>
        Ex(*k ) i   jk1 N1 k1 l N1 M  Xo  j    Xo l    G(((kjN)1)N  ) i 1 N  1 
S(((kjN)1)N  ) i 1 N  1  G(((klN1))N  ) i 1 N  1  S(((klN1))N  ) i 1 N  1 
(
        <xref ref-type="bibr" rid="ref25">25</xref>
        )
k N k N
    M Y  j Y  l  G(((kjN)1)N  ) i 1 N  1G(((klN1))N  ) i 1 N  1 
j1  1 l1  1
5 Prognostication on the basis of complete a priori information
about the sequence measured with errors
Application of the operation of filtration in algorithm (
        <xref ref-type="bibr" rid="ref19">19</xref>
        ),(
        <xref ref-type="bibr" rid="ref20">20</xref>
        ) allows to decrease
mean-square error of extrapolation compared with (
        <xref ref-type="bibr" rid="ref11">11</xref>
        ),(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) as the estimation
x*   , =1,k has better accuracy characteristics compared with z   , =1,k . But
in algorithm (
        <xref ref-type="bibr" rid="ref19">19</xref>
        ),(
        <xref ref-type="bibr" rid="ref20">20</xref>
        ) as well as in (
        <xref ref-type="bibr" rid="ref11">11</xref>
        ),(
        <xref ref-type="bibr" rid="ref12">12</xref>
        ) there is a mismatch between stochastic
qualities of a posteriori information x*   ,  =1, k and parameters of extrapolation
form (
        <xref ref-type="bibr" rid="ref5">5</xref>
        ),(
        <xref ref-type="bibr" rid="ref6">6</xref>
        ) on the basis of which the method under study is formed.
      </p>
      <p>For the forming of the method of the prognosis by noisy measurements let’s
introduce into consideration the mixed random sequence
 X   Z 1 , Z 2 ,..., Z  k  , X k 1 ,..., X  I  combining in itself the results of
measurements till i  k , as well as the data about the sequence X  for i  k  1,I .</p>
      <p>The canonical expansion for such a sequence is of the form</p>
      <p>i N
X 'i  M  X 'i    U( ) 1( ) i , i  1, I.</p>
      <p> 1  1</p>
      <p>Random coefficients of the canonical decomposition (26) defined by the following
recurrence formulas:
- for observation interval t1,..., tk </p>
      <p> 1 N  1
U( )  Z    M Z    U( j) (j)    U( j) (j)   ,   1, k;
 1 j1 j1
- for forecasting interval tk 1,..., tI </p>
      <p> 1 N  1
U( )  X     M  X     U( j) (j)    U( j) (j)   ,   k 1, I.</p>
      <p> 1 j1 j1
Accordingly, the expression for the dispersion of the random coefficients
U( ) , =1, N ,   1, I are of the form:
- for observation interval t1,..., tk </p>
      <p>D    M U( ) 2   M Z 2    M 2 Z    </p>
      <p>
          
 1 N 2  1 2
  Dj    (j)     Dj    (j)   ,   1, k;
 1 j1 j1
(26)
(27)
(
        <xref ref-type="bibr" rid="ref26">28</xref>
        )
(
        <xref ref-type="bibr" rid="ref27">29</xref>
        )
- for forecasting interval tk 1,..., tI 
      </p>
      <p>The coordinate functions  h( ) i  are calculated using the formulas:
- for observation interval t1,..., tk  (function  h( ) i  describes the stochastic
relationship between the variables Z    and Z h i  )
 h( ) i  </p>
      <p>1
D  </p>
      <p>M Z    Z h i   M Z    M Z h i  
 1 N  1 
  D j   (j)   h(j) i   D j ( ) (j)   h(j) i  ,   1, h, 1   i  k
 1 j1 j 1 
- for description in the canonical decomposition of stochastic correlation between
intervals t1,..., tk  and tk 1,..., tI  ( h( ) i  describes the relationship between random
variables Z    and X h i  )
 h( ) i  </p>
      <p>1
D  </p>
      <p>M Z    X h i   M Z    M  X h i  
 1 N  1 
  D j   (j)   h(j) i   D j   (j)   h(j) i  ,   1, k , i  k  1, I ;
 1 j1 j 1 
- for forecasting interval tk 1,..., tI  (function  h( ) i  describes the stochastic
relationship between the variables X    and X h i  )
 h( ) i  </p>
      <p>M  X    X h i   M  X    M  X h i  
 1 N  1 
  D j   (j)   h(j) i   D j   (j)   h(j) i  , k   i  I .</p>
      <p> 1 j1 j 1 </p>
      <p>
        The necessity of the two expressions (
        <xref ref-type="bibr" rid="ref26">28</xref>
        ) and (
        <xref ref-type="bibr" rid="ref27">29</xref>
        ) for the determination of the
random coefficients of the canonical expansion (27) is explained with the technology
of the forming of random sequence  X  :  X   Z , ti , i=1,k and  X    X  ,
ti , i=k  1,I . The stated peculiarity also results in the increasing compared to the
expansion (
        <xref ref-type="bibr" rid="ref1">1</xref>
        ) of the number of formulae for the calculation of the dispersions of the
random coefficients (
        <xref ref-type="bibr" rid="ref27">29</xref>
        ), (
        <xref ref-type="bibr" rid="ref28">30</xref>
        ) and coordinate functions (
        <xref ref-type="bibr" rid="ref29">31</xref>
        ),(
        <xref ref-type="bibr" rid="ref30">32</xref>
        ),(33).
      </p>
      <p>In the canonical expansion (26) the random sequence X  is presented in the
investigated range of points ti , i 1,I with the help of N arrays U (  ) ,  1, N of
uncorrelated centered random coefficients U ( ) , i  1, I. The given coefficients contain
i
information
about
the
values</p>
      <p>Z  i  ,   1, N , i  1, k
and
X  i  ,   1, N , i  k  1, I , and coordinate functions  ( ) i ,  , h  1, N ,  , i  1, I
h
describe probabilistic connections of the order   h between sections t

and
t ,  ,i  1,I .
i
tion t :</p>
      <p>1
Let us assume that as a result of measurement in the first point of discretization t
1
value z 1 becomes known (additive mixture of unobserved true value x 1 and error
y 1 ). Measurement z 1 concretizes random coefficients U ( ) ,   1, N for
sec1
u( )  z 1  M Z  1   u( j) ( j) 1 ,   1, N.
1 1 1</p>
      <p>Substitution of values (34) in canonical expansion (26) and further application of
the operation of mathematical expectation allow to write down the expression for the
estimation of future values xh i 
zl 1 , l  1, N in the following form</p>
      <p>with the use of a posteriori information
mx(1/,zl)  h, i  mx(1/,zl1)  h, i    zl 1  mx(1/,zl1) l,1 (l) i 
h1
(34)
(35)
(36)
(37)
where mx(1/,zl)  h, i  is optimal (in mean-square sense) estimation of value xh i 
provided that for the prognosis values z j 1 , j  1, l are used.</p>
      <p>Measurement z  2 leads to the fixation of random coefficients u( ) ,   1, N for
2
t :
2</p>
      <p>Use of the values of random coefficients (36) allows to obtain prognosis algorithm
taking into consideration zl 1 , zl  2 l  1, N :
mx(2/z,l)  h, i   
mx(2/z,l1)  h, i    zl  2  mx(2/z,l1) l, 2 (l) i  , l  1;</p>
      <p>
        h2
 mx(1/,zN ) h, i    z  2  mx(1/,zN ) 1, 2 (
        <xref ref-type="bibr" rid="ref1">1</xref>
        ) i  , l  1.
 h2
      </p>
      <p>For random quantity of measurements z   ,   1, I the algorithm of optimal
extrapolation takes on form:
 M  X h (i) ,   0;


mx(/z,l) (h, i)   mx(/z,l1) (h, i)   zl ( )  mx(/z,l1) (l, ) h(l) (i), l  1;

mx(/z1,N ) (h, i)   zl ( )  mx(/z1,N ) (l, ) h(l) (i), l  1.</p>
      <p>Expression</p>
      <p>mx(/z,l) h, i   M  X h i  / z  j  , j  1, 1,   1, N; z   ,
h  1, l  N ,   k is unbiased optimal estimation mx(k/ z,N 1) 1, i  of future value
x i  , i  k 1, I provided that for the calculation of given estimation values
z  j  ,   1, N , j  1, k are used that is the results of the measurements of sequence
X  in points t j , j  1, k are known.</p>
      <p>In Fig. 1 the diagram is presented that reflects peculiarities of functioning of the
method of prognosis (38).</p>
      <p>Mean-square error of extrapolation with the help of method (39) is determined by the
expression:</p>
      <p>M X i / z  j  ,   1, N , j  1, k   mx(k/z,N ) 1, i 2   M  X 2 i  </p>
      <p>k N 2
M 2  X i    D  j   1(j ) i , i  k 1, I.</p>
      <p>j1  1</p>
    </sec>
    <sec id="sec-3">
      <title>6 Conclusion</title>
      <p>In nowadays, the prognostication of the current state of complex computer systems,
especially, for the class of critical applications, is an important and actual problem for
providing high functioning reliability of the various control objects and
decisionmaking systems. The proposed approach, based on the mathematical formalization of
the parametrical changes of computer systems using nonlinear canonic models of the
random sequences, allows to take into account the stochastic properties of
investigated computer systems. Exhaustive solutions of the prognostication problems are
obtained by authors with the aim of the evaluation of the computer system state and
analysis of its further operational capability in the situations with different volume of
a priori and a posteriori information or with various levels of information uncertainty.
Synthesized prognostication methods as well as assumed, as their basis canonical
expansions do not impose any significant limitations on random sequences
(38)</p>
      <p>for
(39)
)
8
3
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.
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.
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i</p>
      <p>F
of the change of the values of controlled parameters including linearity, stationarity,
Markov behavior, monotoneness, etc. Suggested mathematical expressions for the
determination of mean-square error of extrapolation allow to make a decision about
the choice of the most appropriate method from the totality of the introduced ones for
the solution of the prognostication problem of computer system with prescribed
accuracy. The specific diagram, presented in the paper, reflects the peculiarities of the
synthesized prognostication methods. Proposed methods are fairly simple in
computing aspects and may be applied for solving computer system prognostication tasks in
real time taking into account that all parameters of the prognostication models can be
defined previously.</p>
    </sec>
  </body>
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