Multiply matrix by each element of a vector without a for loop

If I have a matrix A and a vector v filled with scalars, how to I multiply A by each element of v, storing each result in an array as I go without using a for loop.

For example, if I have

A = [1,1;1,1]
v = [1,2,3]

I want to get an array M that is

M = {[A.*v(1)],[A.*v(2)],[A.*v(3)]} = {[1,1;1,1],[2,2;2,2],[3,3;3,3]}

Is there any way to do this without a for loop?

Answer 1

[Star Strider]

This may be considered ‘cheating’, however it does meet the requirements:

A = [1,1;1,1];
v = [1,2,3];
vr = repelem(v,2,2)

vr = 2×6

1 1 2 2 3 3 1 1 2 2 3 3

Ar = repmat(A,1,3)

Ar = 2×6

1 1 1 1 1 1 1 1 1 1 1 1

M = Ar.*vr

M = 2×6

1 1 2 2 3 3 1 1 2 2 3 3

Mc = mat2cell(M,2,ones(1,3)*2)

Mc = 1×3 cell array
    {2×2 double}    {2×2 double}    {2×2 double}

Mc{1}

ans = 2×2

1 1 1 1

Mc{2}

ans = 2×2

2 2 2 2

Mc{3}

ans = 2×2

3 3 3 3

Generalising this to a different ‘A’:

A2 = [1 2; 3 4];
A2r = repmat(A2,1,3)

A2r = 2×6

1 2 1 2 1 2 3 4 3 4 3 4

M2 = A2r.*vr

M2 = 2×6

1 2 2 4 3 6 3 4 6 8 9 12

See the documentation for repmat, repelem, and mat2cell for details.

.

Answer 2

[Stephen23]

Let MATLAB do the heavy lifiting for you! Note that RESHAPE operations are computationally cheap as they do not change the array data themselves, just some of the mxArray meta-data.

A = [1,1;1,1];
v = [1,2,3];
C = num2cell(A.*reshape(v,1,1,[]),1:2);
C{:}

ans = 2×2

1 1 1 1

ans = 2×2

2 2 2 2

ans = 2×2

3 3 3 3

Answer 3

[Steven Lord]

A = [1,1;1,1];
v = [1,2,3];
R = pagemtimes(A, reshape(v, 1, 1, []))

R = 
R(:,:,1) =

     1     1
     1     1


R(:,:,2) =

     2     2
     2     2


R(:,:,3) =

     3     3
     3     3