MATLAB: Symbolic Math expression simplification

circuitcomplexsymbolic

Hello,

I am trying to simplify a symbolic expression, in terms of others,for example:

syms w L C;
Z = 1j*w*L + 1/(1j*w*C)

Ok, the result is (-w^2LC + 1)/(1jwC)

The question is, for example, if I want to simplify the result so that Matlab substitutes -w^2LC+1 for a variable like 'RF1', what should I do?

The simulation I am running outputs several (more than 100) combination from a complex ckt topology, many or all the combinations results could be simplified to Freq1, IntrisicImpedance, etc.

All the Best.

Ronaldo

Best Answer

http://www.mathworks.com/help/symbolic/subexpr.html

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MATLAB: “Substitution function” by symbolic math toolbox

doc subs %?

MATLAB: How to substitute a sub-expression in a symbolic expression using Symbolic Math Toolbox 5.4 (R2010a)

This enhancement has been incorporated in Release 2013a (R2013a). For previous product releases, read below for any possible workarounds:

In Symbolic Math Toolbox 5.4 (R2010a), SUBS can only be used to substitute a variable in an expression with another variable or expression. SUBS may not be used to substitute a sub-expression in an expression.

As a workaround, you can use SUBSEX, available in the MuPAD language, to substitute a sub-expression in an expression. You may call this function with the help of FEVAL as follows:

q = feval(symengine,'subsex',u,[char(w0) '=w0'])
q =
a*cos(t*w0 + 3) + b*sin(5*t*w0 + 3)

You can also create an anonymous function to mimic SUBS:

subsx = @(u,w0,w0str) feval(symengine,'subsex',u,[char(w0) '=' w0str]);
%then issuing the command: 
p3 = subsx(u, w0, 'w0')

You may read more about SUBSEX in the MuPAD help documentation at:

 <http://www.mathworks.com/help/releases/R2013a/symbolic/mupad_ref/subsex.html>

Best Answer

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MATLAB: “Substitution function” by symbolic math toolbox

MATLAB: How to substitute a sub-expression in a symbolic expression using Symbolic Math Toolbox 5.4 (R2010a)

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