How does symvar work?

Hi all!

symvar 'cos(2*pi*t)'

How can I make symvar to not return 't'?

I use this: syms t

but no success.

Answer 1

[Paulo Silva]

symvar gives you the symbolic variables inside one expression, you say that t is symbolic so the expression symvar('cos(2*pi*t)') gives you t, I can't imagine why you don't wan't to get the t.

[sadel]

Well here is my main problem: http://www.mathworks.com/matlabcentral/answers/8905-how-can-i-create-a-function-which-evaluate-only-strings-which-represent-only-mathematical-functions

I saw that symvar returns identifiers other than i, j, pi, inf, nan, eps, and common functions and I believe that if I make it to identify the 't' from a string like this 'cos(2*pi*t)' , then I can reach my target

[sadel]

If I could make symvar to identify the symbol 't' and doesn't return it then I could create

a function which evaluate only strings which represent only mathematical functions

t=0:0.1:10;

insertfunction='cos(2*pi*t))'

gh=symvar(insertfunction)

if (gh is an empty cell array)

eval(['v =0*t+ ',vectorize(gh),';'])

plot(t,v)

end

[Paulo Silva]

t=0:0.1:10;

insertfunction='cos(2*pi*t))'

gh=symvar(insertfunction)

if (numel(gh)==1) %see if there's only one symbolic variable (just the t)

eval(['v =0*t+ ',vectorize(gh),';'])

plot(t,v)

end