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I would like to multiply an array by each element of another array, and am having a lot of trouble finding a built-in or automated method of doing.

Here is an example of what I'd like to achieve:

a = 0.5;
b = 4.0;

mat = {{0, 1}, {a, b}};
Rmat = RandomInteger[10, {4, 4}]
m11 = mat[[1, 1]]*Rmat;
m12 = mat[[1, 2]]*Rmat;
m21 = mat[[2, 1]]*Rmat;
m22 = mat[[2, 2]]*Rmat;

fmat = ArrayFlatten[{{m11, m12}, {m21, m22}}]

As you can see, the first matrix mat is multiplied by each individual element of Rmat. I feel like this should be easy, but I'm not finding a built-in function that works?

Thanks!

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3 Answers 3

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ArrayFlatten[Outer[Times, mat, Rmat]]
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  • $\begingroup$ Those both work thanks! $\endgroup$
    – gKirkland
    Commented Mar 7, 2014 at 4:16
  • $\begingroup$ @rasher...good old Outer,+1 $\endgroup$
    – ubpdqn
    Commented Mar 7, 2014 at 4:45
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Try this:

ArrayFlatten[Map[Rmat*# &, mat, {2}]]
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It was apparently missed by the other posters that KroneckerProduct[] is built-in:

KroneckerProduct[mat, Rmat]
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  • $\begingroup$ Yep. Forgot it.... $\endgroup$
    – ciao
    Commented Aug 21, 2015 at 19:57
  • $\begingroup$ J.M Could you help me question if you have time now? Please see here and here $\endgroup$
    – xyz
    Commented Aug 22, 2015 at 7:40
  • $\begingroup$ @Shutao, not sure what those pictures are supposed to be. Why not write a proper question instead of a comment? $\endgroup$
    – J. M.'s missing motivation ♦
    Commented Aug 22, 2015 at 8:11
  • $\begingroup$ @Guesswhoitis. I think this small question could be solved in the chatting room. $\endgroup$
    – xyz
    Commented Aug 22, 2015 at 8:14
  • $\begingroup$ Maybe this picture can express what I need. $\endgroup$
    – xyz
    Commented Aug 22, 2015 at 8:22

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