MATLAB: How to replace some symbolic values in a matrix

subssymbolic

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!

Best Answer

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})

Related Solutions

MATLAB: Trouble using ezplot and matlabFunction on a symbolic function defined using symengine “piecewise”

If you have R2016b and the Symbolic Math Toolbox installed, you can just use the piecewise function:

https://www.mathworks.com/help/symbolic/piecewise.html

For example:

MATLAB: Converting a symbolic matrix to a normal matrix

Try this:

syms x y z
M = jacobian([x*y*z, y^2, x + z], [x, y, z]);
M = subs(M, {x,y,z},{1,1,1});
dM = double(M);

You can also create ‘M’ as a symbolic function:

syms x y z
M(x,y,z) = jacobian([x*y*z, y^2, x + z], [x, y, z]);
nM = M(1,1,1);
dM = double(nM);

The result is the same.

Best Answer

Related Solutions

MATLAB: Trouble using ezplot and matlabFunction on a symbolic function defined using symengine “piecewise”

MATLAB: Converting a symbolic matrix to a normal matrix

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