How does symvar work?

2011 6 7
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Hi all!
symvar 'cos(2*pi*t)'
How can I make symvar to not return 't'?
I use this: syms t
but no success.

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Paulo Silva
Paulo Silva 2011-6-7

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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.

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sadel
sadel 2011-6-7
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
sadel 2011-6-7
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
Paulo Silva 2011-6-9
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

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