How to perform elementwise multiplication between two matrices with different size or summation between two matrices with the same size

Hello, imagine I have the following array:

f = 1:10;
x = -22:1:22;
y = -22:1:22;
[u,v] = meshgrid(x,y);

I wish to perform elementwise multiplication operation between 'f' and 'u' (I mean the final array must have numel(f)*numel(u) elements.) . How can I fo this efficiently (definitely I know how to do this using "for loop". this is time consuming.)? Moreover, Imagine that I want to sum "u" and "v" elementwisely which both of them have the same size (so the final array must have numel(u)*numel(v) elements.) . How to do this in order to have high speed?

Answer 1

[Steven Lord]

Let's look at the sizes of the arrays in question.

f = 1:10;
x = -22:1:22;
y = -22:1:22;
[u,v] = meshgrid(x,y);
whos f x y u v

  Name       Size            Bytes  Class     Attributes

  f          1x10               80  double              
  u         45x45            16200  double              
  v         45x45            16200  double              
  x          1x45              360  double              
  y          1x45              360  double              

I wish to perform elementwise multiplication operation between 'f' and 'u' (I mean the final array must have numel(f)*numel(u) elements.)

So do you specifically want the size of the output to be [10 45*45] = [10, 2025]? Since you're using a release that supports implicit expansion this is not that difficult.

A = reshape(f, numel(f), 1).*reshape(u, 1, numel(u));
whos A

  Name       Size               Bytes  Class     Attributes

  A         10x2025            162000  double              

How can I fo this efficiently (definitely I know how to do this using "for loop". this is time consuming.)? Moreover, Imagine that I want to sum "u" and "v" elementwisely which both of them have the same size (so the final array must have numel(u)*numel(v) elements.) . How to do this in order to have high speed?

So you want to just normally add u and v?

B = u+v;
whos B

  Name       Size            Bytes  Class     Attributes

  B         45x45            16200  double              

Or do you want to add each element of u to each element of v, not just corresponding elements?

C = reshape(u, numel(u), 1) + reshape(v, 1, numel(v));
whos C

  Name         Size                 Bytes  Class     Attributes

  C         2025x2025            32805000  double              

[moh mor]

thank you

Answer 2

[Voss]

f = 1:10;
x = -22:1:22;
y = -22:1:22;
[u,v] = meshgrid(x,y);
whos

  Name         Size            Bytes  Class     Attributes

  cmdout       1x33               66  char                
  f            1x10               80  double              
  u           45x45            16200  double              
  v           45x45            16200  double              
  x            1x45              360  double              
  y            1x45              360  double              

Note that u and v are 45x45 matrices, so each has 2025 elements.

Something along these lines may be what you are looking for:

fu = f(:).*u(:).'

fu = 10×2025

-22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -22 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -44 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -66 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -88 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -132 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -154 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -176 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -198 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220 -220

uv = u(:)+v(:).'

uv = 2025×2025

-44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15 -44 -43 -42 -41 -40 -39 -38 -37 -36 -35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -15

[moh mor]

thank you

[Voss]

You're welcome!