# Unable to perform assignment because the left and right sides have a different number of elements.

1 view (last 30 days)
Zixin Zhou on 25 Nov 2020
Answered: Walter Roberson on 25 Nov 2020
I would like to use code of SOR method. Here is the code:
% SOR ALGORITHM 7.3
%
% To solve Ax = b given the parameter w and an initial approximation
% x(0):
%
% INPUT: the number of equations and unknowns n; the entries
% A(I,J), 1<=I, J<=n, of the matrix A; the entries
% B(I), 1<=I<=n, of the inhomogeneous term b; the
% entries XO(I), 1<=I<=n, of x(0); tolerance TOL;
% maximum number of iterations N; parameter w (omega).
%
% OUTPUT: the approximate solution X(1),...,X(n) or a message
% that the number of iterations was exceeded.
syms('OK', 'AA', 'NAME', 'INP', 'N', 'I', 'J', 'A', 'X1');
syms('TOL', 'NN', 'W', 'K', 'ERR', 'S', 'FLAG', 'OUP');
TRUE = 1;
FALSE = 0;
fprintf(1,'This is the SOR Method for Linear Systems.\n');
OK = FALSE;
fprintf(1,'The array will be input from a text file in the order:\n');
fprintf(1,'A(1,1), A(1,2), ..., A(1,n+1) \n');
fprintf(1,'A(2,1), A(2,2), ..., A(2,n+1),\n');
fprintf(1,'..., A(n,1), A(n,2), ..., A(n,n+1)\n\n');
fprintf(1,'Place as many entries as desired on each line, but \n');
fprintf(1,'separate entries with at least one blank.\n');
fprintf(1,'The initial approximation should follow in same format.\n\n\n');
fprintf(1,'Has the input file been created? - enter Y or N.\n');
AA = input(' ','s');
if AA == 'Y' | AA == 'y'
fprintf(1,'Input the file name in the form - drive:\\name.ext\n');
fprintf(1,'for example: A:\\DATA.DTA\n');
NAME = input(' ','s');
INP = fopen(NAME,'rt');
OK = FALSE;
while OK == FALSE
fprintf(1,'Input the number of equations - an integer.\n');
N = input(' ');
if N > 0
A = zeros(N,N+1);
X1 = zeros(1,N);
for I = 1 : N
for J = 1 : N+1
A(I,J) = fscanf(INP, '%f',1);
end;
end;
for I = 1 : N
X1(I) = fscanf(INP, '%f',1);
end;
% use X1 for X0
OK = TRUE;
fclose(INP);
else
fprintf(1,'The number must be a positive integer.\n');
end;
end;
OK = FALSE;
while OK == FALSE
fprintf(1,'Input the tolerance.\n');
TOL = input(' ');
if TOL > 0
OK = TRUE;
else
fprintf(1,'Tolerance must be a positive number.\n');
end;
end;
OK = FALSE;
while OK == FALSE
fprintf(1,'Input maximum number of iterations.\n');
NN = input(' ');
if NN > 0
OK = TRUE;
else
fprintf(1,'Number must be a positive integer.\n');
end;
end;
fprintf(1,'Input parameter w (omega)\n');
W = input(' ');
% use W for omega
else
fprintf(1,'The program will end so the input file can be created.\n');
end;
if OK == TRUE
% STEP 1
K = 1;
OK = FALSE;
% STEP 2
while OK == FALSE & K <= NN
% ERR is used to test accuracy - it measures the infinity norm
ERR = 0;
% STEP 3
for I = 1 : N
S = 0;
for J = 1 : N
S = S-A(I,J)*X1(J);
end;
S = W*(S+A(I,N+1))/A(I,I);
if abs(S) > ERR
ERR = abs(S);
end;
X1(I) = X1(I)+S;
end;
% STEP 4
if ERR <= TOL
OK = TRUE;
% process is complete
else
% STEP 5
K = K+1;
% STEP 6 - is not used since only one vector is required
end;
end;
if OK == FALSE
fprintf(1,'Maximum Number of Iterations Exceeded.\n');
% STEP 7
% procedure completed unsuccessfully
else
fprintf(1,'Choice of output method:\n');
fprintf(1,'1. Output to screen\n');
fprintf(1,'2. Output to text file\n');
FLAG = input(' ');
if FLAG == 2
fprintf(1,'Input the file name in the form - drive:\\name.ext\n');
fprintf(1,'for example: A:\\OUTPUT.DTA\n');
NAME = input(' ','s');
OUP = fopen(NAME,'wt');
else
OUP = 1;
end;
fprintf(OUP, 'SOR ITERATIVE METHOD FOR LINEAR SYSTEMS\n\n');
fprintf(OUP, 'The solution vector is :\n');
for I = 1 : N
fprintf(OUP, ' %11.8f', X1(I));
end;
fprintf(OUP, '\nusing %d iterations with\n', K);
fprintf(OUP, 'Tolerance %.10e in infinity-norm\n', TOL);
fprintf(OUP, 'with Parameter %.10e\n', W);
if OUP ~= 1
fclose(OUP);
fprintf(1,'Output file %s created successfully \n',NAME);
end;
end;
end;
And my data matrix is:
1 -0.5 0 0 0 0 0
-0.5 1 -0.5 0 0 0 0
0 -0.5 1 -0.5 0 0 0
0 0 -0.5 1 -0.5 0 0
0 0 0 -0.5 1 -0.5 0
0 0 0 0 -0.5 1 -0.5
0 0 0 0 0 -0.5 1
But I got error like this:
Has the input file been created? - enter Y or N.
Y
Input the file name in the form - drive:\name.ext
for example: A:\DATA.DTA
ALG073.DTA
Input the number of equations - an integer.
7
Unable to perform assignment because the left and right sides have a different number of elements.
Error in ALG073 (line 47)
X1(I) = fscanf(INP, '%f',1);
Can anyone help?

Walter Roberson on 25 Nov 2020
When you enter 7 then the code expects to read 7 lines with 8 values per line (though as the prompts hint you can put as many values per line as you want, but the order will be groups of 8 values go into each row)
After that the file needs 7 numeric initial values.
The data matrix you posted is only 7x7 not 7x8. If your file then what you intend as 7 initial values they would be read in as the rest of the A values. Then when the code went to read the initial values it would not find any.