syms back to numbers

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Philosophaie
Philosophaie 2014-2-4
评论： Walter Roberson 2014-2-5
I am using syms to calculate equations with derivatives. I need to assign these syms number values to complete the analysis.
syms x y z
f=x^3 - 2 * y^4 + 4 * z^2
x=4
y=3
z=5
f=

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回答（1 个）

Sean de Wolski
Sean de Wolski 2014-2-4
Use subs to substitute the values in:
syms x y z
f=x^3 - 2 * y^4 + 4 * z^2
subs(f,{x,y,z},{4,3,5})
And
http://www.mathworks.com/help/releases/R2013b/symbolic/subs.html
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Philosophaie
Philosophaie 2014-2-4
Actually g_ did evaluate correctly, a 4x4.
The problem came in Affinity, a 4x4x4 with an error code:
??? Error using ==> maple
Error, (in index/FillInitVals) array defined with 1 indices, used with 3 indices
Error in ==> sym.subs at 229
NEWf = sym(maple('evalm',strrep(NEWf,'MATRIX','array')));
Error in ==> SchwarzchildAnalysis_Excel>Evaluate at 65
subs(Affinity,{r,h,p,t},{rr,theta,phi,tt})
Walter Roberson
Walter Roberson 2014-2-5
What does Affinity look like before substitution? And please cross-check that rr, theta, phi, and tt are all scalars.

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