How to multiply two matrices

Hello i have two matrices.

1. a 2749*1 matrix
2. a 500*1 matrix

i want to multiply above matrices like this

• first 500 rows of 1st matrix with 2nd matrix and store the value
• jump 250 rows (now we are in 750th row)
• then 2nd 500 rows (from 750th row to 1250th row) of 1st matrix with 2nd matrix and store the valuelikewise.you have to get the transpose of the first matrix to match the dimension to multiply. (1*500 and 500*1)

[John D'Errico]

So I am forced to wonder why two people are asking virtually the same question. Sounds like homework to me.

Answer 1

[Michael Saniuk]

>> A = rand(2749,1);
>> B = rand(500,1);
>> C = A(1:500,1).*B;
>> D = A(751:1250,1).*B;

Answer 2

[Star Strider]

What output do you want from your vector multiplication?

Try this:

A = randi(9, 1, 2500);                                          % Create Data
B = randi(9, 500, 1);                                           % Create Data
for k1 = 1:2
    Result(:,k1) = A(1, (1:500)+(k1-1)*250).' .* B;
end

This does element-wise multiplication, producing a vector in ‘Result’. If you want a single value (dot-product), change ‘.*’ to ‘*’.

Answer 3

[Andrei Bobrov]

A - vector 2749 x 1

B - vector 500 x 1

A1 = reshape(A(1:2*749),749,[]);
out = A1(1:500,:).' * B;               % dot-product
out = A1(1:500,:) .* B;                % element-wise MATLAB >=R2016b
out = bsxfun(@times,A1(1:500,:),B);    % element-wise MATLAB >=R2016b