Help ,urgent.
2 views (last 30 days)
Show older comments
Anshuman S
on 14 Jun 2017
Answered: Walter Roberson
on 14 Jun 2017
Hi this error is being generated:
In an assignment A(:) = B, the number of elements in A and B must be the same.
Error in q1_gs_150115 (line 42)
x(k) = num/At(k,k);
My code :
function [GS] = q1_gs_150115(~)
m=input('variables');
r=input('relaxation_number');
for i=1:m
for j=1:m
A(i,j)=input('element_i,j');
end
end
A=reshape(A,m,m);
for i = 1:m
j = 1:m;
j(i) = [];
B = abs(A(i,j));
c(i) = abs(A(i,i)) - sum(B); % Is the diagonal value greater than the remaining row values combined?
if c(i) > 0
fprintf('The matrix is diagonally dominant at row %2i\n\n',i)
end
end
for i=1:m
s(i,1)=input('constants_i');
end
p=input('number_of_iterations');
for i=1:m
x(i,1)=input('initial_values_i');
end
err = zeros(m,1);
At = [A,s];
for iter = 1:p
for k = 1:m
xold = x(k);
num = (1-r)*At(k,k)*x(k+1:m)+ r*At(k,end) - r*At(k,1:k-1)*x(1:k-1) - r*At(k,k+1:m)*x(k+1:m);
x(k) = r*num/At(k,k);
err(k) = abs(x(k)-xold);
end
disp(['Iter ',num2str(iter), '; Error =', num2str(max(err))]);
end
disp('The result is:')
disp(x)
2 Comments
Guillaume
on 14 Jun 2017
Doubly ironical, since you haven't posted the relevant information for us to even give you an answer.
Accepted Answer
Walter Roberson
on 14 Jun 2017
num = (1-r)*At(k,k)*x(k+1:m)+ r*At(k,end) - r*At(k,1:k-1)*x(1:k-1) - r*At(k,k+1:m)*x(k+1:m);
r is a scaar. At(k,k) is a scalar. At(k,end) is a scalar. x(k+1:m) is a column vector. So we have to conclude that (1-r)*At(k,k)*x(k+1:m) is a column vector.
At(k,1:k-1) is a row vector but it is being used with "*" against a column vector, so the result of the "*" is a scalar, so r*At(k,1:k-1)*x(1:k-1) is a scalar.
At(k,k+1:m) is a row vector, but it is being used with "*" against a column vector, so the result of the "*" is a scalar, so r*At(k,k+1:m)*x(k+1:m) is a scalar.
num is therefore column vector minus scalar minus scalar. That is going to give a column vector result.
Then in the next line,
x(k) = r*num/At(k,k);
r is a scalar, At(k,k) is a scalar, and we found from above that num is a column vector. r*num/At(k,k) must therefore be a column vector. But you are trying to store the column vector into a scalar location, x(k)
0 Comments
More Answers (0)
See Also
Categories
Find more on Matrices and Arrays in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!