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

2 次查看（过去 30 天）
Matthew Crowther
Matthew Crowther 2021-7-7
编辑： Stephen23 2021-7-7
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?

请先登录，再回答此问题。

回答（3 个）

Star Strider
Star Strider 2021-7-7
Ran in:
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.
.
Stephen23
Stephen23 2021-7-7
编辑：Stephen23 2021-7-7
Ran in:
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
Steven Lord
Steven Lord 2021-7-7
Ran in:
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

类别

在 Help Center 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by