syms back to numbers

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=

Answer 1

[Sean de Wolski]

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

[Philosophaie]

subs(f,{x,y,z},{4,3,5})

does not work if " f " is a 4x4, a 4x4x4 or a 4x4x4x4 array

[Sean de Wolski]

huh?

Please provide a minimal working example.

[Philosophaie]

 syms r h p t

m=constant

g_ = [1/(1-2*m/r) 0 0 0;0 r^2 0 0;0 0 r^2*(sin(h))^2,0;0,0,0,-(1-2*m/r)]

      rr = exlSheet1.Range(['C' num2str(5)]).value;

      theta = exlSheet1.Range(['D' num2str(5)]).value;

      phi = exlSheet1.Range(['E' num2str(5)]).value;

      tt = exlSheet1.Range(['F' num2str(5)]).value;

      subs(g_,{r,h,p,t},{rr,theta,phi,tt})

[Walter Roberson]

There does not appear to be any "p" or "t" in your g_ ?

What values are you extracting for the variables, and what result do you get for the substitution, and what result are you expecting for the substitution ?

[Philosophaie]

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]

What does Affinity look like before substitution? And please cross-check that rr, theta, phi, and tt are all scalars.