MATLAB: Code for elements in equation to create a matrix

matrix

D is a 1×3 matrix

f is a 3×3 matrix

I want to create a matrix of A by the following equation:

for j=1:3

for i=1:3

A(i)=(sum(D(j).*f(i,j)))^-1;

end

But it turns out that the answer is wrong

What should be the correct code of this equation?

Best Answer

Lo, no need to use loops:

 A = 1./(f*D)

Make sure that D is a column vector.

Related Solutions

MATLAB: How to replace the following code, to get the matrix

You really just need to make a sparse diagonal matrix. This can very easily be done with spdiags. Use the last syntax: A = spdiags(B,d,m,n), which you would be calling as: A = spdiags(B,d,n^2,n^2);. The issue now is only in setting up B and d which really just requires you to replace a few values in each of the columns of B, but this can be done by finding the appropriate indices to replace (note that not all values in B will be used, so start your counting from the bottom as this function will omit unnecessary values at the top of the matrix B). Put your head to the grindstone and I'm sure you can find the patterns necessary to do this for arbitrary values of n, without loops or cell arrays. I will do it for just for the lowest diagonal:

n = 5; % Change it to 4 and verify the code works in both cases.
B = 0.298*ones(n^2,1); % Use the calculation of wherever 0.298 came from if you wish
d = -(n+1); % The diagonal where the 1st vector of B should appear
B(end-n:-n:1) = 0;
A = spdiags(B,d,n^2,n^2); % This has the lower diagonal
Q = full(A); % For visualizing the correct results.
open Q

Now, just add the columns for the other diagonals to B and add the diagonal identifier to d. Also, never use the line of code:

if true
   %code
end

true is always true so the code always runs.

MATLAB: Element in matrix multiplication to create a new matrix

Your code doesn't run because you are using .* which is element wise multiplication instead of standar matrix multiplication. You can do:

for i=1:3
    for j=1:3
        T(i,j)=A(i).*B(j).*O(i).*D(j).*f(i,j)
    end
end

T=A*B*O*D*f

depending on the result you are expecting.

Best Answer

Related Solutions

MATLAB: How to replace the following code, to get the matrix

MATLAB: Element in matrix multiplication to create a new matrix

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