Clarification regarding a usage in matlab

Question

Suppose that I type the following code in matlab command window :

>> f=dsolve('D2y+y=0','y(0)=0',x)

So I get this :

>>f=
C22*sin(x)

Suppose from this I want to extract only 'sin(x)' without that C22 how do I do that ?? One more thing is I cannot add any more initial or boundary condition. Please help. Thanks

Answer 1

This code substitues all variables except those in vars_to_keep with 1

syms x
f=dsolve('D2y+y=0','y(0)=0',x);
all_vars=symvar(f);
vars_to_keep=x;
set_to_one=setdiff(all_vars,vars_to_keep);
for ix=1:numel(set_to_one)
    f=subs(f,set_to_one(ix),1);
end