Multiplying 2 Matrices A and B from Scratch (not built in function

How can i write a matlab function which accepts two Matrices A and B and from scratch(indexing - not built in functions) multiplies them together. in the case that they can not be multiplied together simply return an empty matrix ([])

[dpb]

Obviously homework...show your work to date and where, specifically, you got stuck on a Matlab-related question.

Of course, you start with the definition of what matrix multiplication is...

Answer 1

[Manvi Goel]

Here you go

function result =  mult(a, b)
    [r1, c1] = size(a);
    [r2, c2] = size(b); 
    if( c1 == r2)
        result = zeros(r1, c2);
        for i  = 1: r1
           for j =1:c2
              for k = 1:r2
                  result(i,j) = result(i,j) + a(i,k) * b(k,j);
              end
           end
        end
    else
        result = [];
    end
    disp(result)
end

[madhan ravi]

Providing a complete solution to a homework problem is totally not recommended in this forum.

[Mark]

@madhan buzzkill

[Walter Roberson]

It's okay in this case, because the provided code is incorrect.

Answer 2

[Aniket]

function C = matrixMultiply(A, B)
n = size(A,1);
C=zeros(n,n);
for i=1:n
    for j=1:n
        sum=0;
        for k=1:n
            sum=sum+A(i,k)*B(k,j);
        end
        C(i,j)=sum;
    end
end
end

[Aniket]

I find this to be the simplest way to solve this problem.

[Walter Roberson]

C=zeros(n,n);

That code is incorrect. Multiplying an n x m matrix by an m x p matrix should generate an n x p matrix.

[Walter Roberson]

Let's test.

A = [1 2; 3 4]; B = [2 3 4; 5 6 7]; C = [8; 9];
A*B

ans = 2×3

12 15 18 26 33 40

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matrixMultiply(A,B)

ans = 2×2

12 15 26 33

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A*C

ans = 2×1

26 60

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matrixMultiply(A,C)

Index in position 2 exceeds array bounds. Index must not exceed 1.

Error in solution>matrixMultiply (line 15)
sum=sum+A(i,k)*B(k,j);

function C = matrixMultiply(A, B)
n = size(A,1);
C=zeros(n,n);
for i=1:n
    for j=1:n
        sum=0;
        for k=1:n
            sum=sum+A(i,k)*B(k,j);
        end
        C(i,j)=sum;
    end
end
end