I have to follow a specific algorithm for this code but my L and U are coming out as single digits, not matrix and I am not sure why/ how to do that (algorithm is attached as picture)

function [L, U] = crout_LU( A ) %this function decomposes matrix A into a lower triangular matrix L and an %upper triangular matrix U, using Crout's method such that LU = A % A = matrix of coefficients % U = upper triangular matrix % L = lower triangular matrix

[r,c] = size(A); n = length(r); L = zeros(n); U = eye(n);

if r ~= c error('A is not a square matrix') elseif any(diag(A) == 0) warning('diagnol element of is 0') end

for k = 1:n L(k,1)=A(k,1); U(k,k)=1; for i = 2:n U(1,k)=A(1,k)/L(1,1); end

    for i = k:n
        sum_i = 0;
        for m = 1: k - 1
           sum_i = sum_i + L(i,m)*k(m,k);
        end

        L(i,k) = A(i,k) - sum_i;
    end

    for j = k+1:n
        sum_j = 0;
        for z = 1: k-1
            sum_j = sum_j + L(k,z)*U(z,j);
        end

        U(k,j) = (A(k,j) - sum_j)/L(k,k);
    end                       
end

end

Answer 1

[David Goodmanson]

Hi Melissa, you have

[r c] = size(A); n = length(r)

but r is just a scalar that tells you the number of rows in A, so length(r) = 1 and n is set to 1 which of course is not correct.

As a simple alternative to the debugger, it's easy to take semicolons off of the ends of lines to see what is going on. That leads to the problem pretty quickly.