How can I replace some symbolic values in a matrix?

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Hello!

I have a (symbolic) matrix A and its components depend on some symbolic variables (x, y and z). I want to replace the symbolic values with zero and I used subs function:

A = subs(subs(subs(A, x, 0), y, 0), z, 0);

and it doesn’t work (the replacement don’t take place) It doesn’t work either:

A = subs(A, x, 0);

What can I do to replace my symbolic variables with zero in this case?

Thanks!

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Dishant Arora 2014-3-4

The replacement doesn't take place, then what do you get?? It should work fine.

Dina Irofti 2014-3-4

The same matrix A, with the symbolic elements unreplaced

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Answer 1

Walter Roberson 2014-3-4

在 MATLAB Online 中打开

1 个投票

Did you assign a value to x, y, or z at the MATLAB level? If so then when it is the value of x, y, or z that is going to be used in the subs(), not the symbol. You might be able to use

subs(A, {sym('x'), sym('y'), sym('z')}, {0, 0, 0})

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Dina Irofti 2014-3-5

在 MATLAB Online 中打开

This is the error

Error using mupadmex
Error in MuPAD command: Invalid variable. [stdlib::diff]
Error in sym/subs>mupadsubs (line 146)
G = mupadmex('symobj::fullsubs',F.s,X2,Y2);
Error in sym/subs (line 119)
    G = mupadsubs(F,X,Y);

Version: R2012a

Dina Irofti 2014-3-6

You were right: it works if I use another version of Matlab.

Thanks!

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