Saving a matrix with a variable that could take any value

Hi guys,

I would like to save a matrix, by where there is a variable that could take on any value. This is the matrix I would like to save and call up in any script at any time:

SM = [12/L^3 6/L^2 -12/L^3 6/L^2;
     4/L -6/L^2 2/L 6/L^2;
     -12/L^3 -6/L^2 12/L^3 -6/L^2;
     2/L -6/L^2 4/L 6/L^2]

The variable in this case is 'L'.

How can I do this?

Many thanks!

Answer 1

[Torsten]

Either define the matrix as a function handle

SM = @(L)[12/L^3 6/L^2 -12/L^3 6/L^2;
          4/L -6/L^2 2/L 6/L^2;
         -12/L^3 -6/L^2 12/L^3 -6/L^2;
         2/L -6/L^2 4/L 6/L^2];
SM(2)

ans = 4×4

1.5000 1.5000 -1.5000 1.5000 2.0000 -1.5000 1.0000 1.5000 -1.5000 -1.5000 1.5000 -1.5000 1.0000 -1.5000 2.0000 1.5000

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or as a function

Lmat = matrix(2)

Lmat = 4×4

1.5000 1.5000 -1.5000 1.5000 2.0000 -1.5000 1.0000 1.5000 -1.5000 -1.5000 1.5000 -1.5000 1.0000 -1.5000 2.0000 1.5000

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function Lmat = matrix(L)
  Lmat = [12/L^3 6/L^2 -12/L^3 6/L^2;
          4/L -6/L^2 2/L 6/L^2;
          -12/L^3 -6/L^2 12/L^3 -6/L^2;
          2/L -6/L^2 4/L 6/L^2];
end

If you save the function as "matrix.m" in your working directory, it can be called from any script at any time.

[Scott Banks]

Thank you, Torsten!

Answer 2

[dpb]

The matrix is undefined unless and until L is defined -- barring symbolic variable.

The easiest solution it would appear would be to create it as an anonymous function

SM = @(L)[12/L^3  6/L^2 -12/L^3  6/L^2;
           4/L   -6/L^2   2/L    6/L^2;
         -12/L^3 -6/L^2  12/L^3 -6/L^2;
           2/L   -6/L^2  4/L     6/L^2];
L=1;
M=SM(L)

M = 4×4

12 6 -12 6 4 -6 2 6 -12 -6 12 -6 2 -6 4 6

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You can save/load SM at will to evaluate when needed with whatever L is needed...

L=pi;
M=SM(L)

M = 4×4

0.3870 0.6079 -0.3870 0.6079 1.2732 -0.6079 0.6366 0.6079 -0.3870 -0.6079 0.3870 -0.6079 0.6366 -0.6079 1.2732 0.6079

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[Scott Banks]

Thank you, dpb!