The issue is your Subs objects. They are used to represent derivatives at points (like f'(0)), but since your point is a variable, you can just replace Subs(Derivative(f(_xi_1), _xi_1), (_xi_1,), (xi,)) with Derivative(f(xi), xi). To do this, use
temp = temp.doit() If you do that, your solve() line will work. The match line doesn't work because match matches the entire expression, not subexpressions (you want temp.find() if you want that). But I think solve() is what you want, since you want to move f'(xi) to one side of the equation. Aaron Meurer On Mon, Dec 30, 2013 at 10:27 AM, almog yalin <[email protected]> wrote: > I have this partial differential equation > http://en.wikipedia.org/wiki/Burgers%27_equation > To which I want to substitute an ansatz that depends just on one variable: > f(xi), where xi is a function of the two independent variables x and t. > After the substitution, I would like to isolate the derivative d(f)/d(xi). > > I tried writing a script to do it, but I can't refer to the relevant > derivative. > Attached herein is the script. Here's the output I get: > > (-nu*xi**3*Subs(Derivative(f(_xi_1), _xi_1), (_xi_1,), (xi,))/2 - > nu*xi**2*Subs(Derivative(f(_xi_1), _xi_1, _xi_1), (_xi_1,), (xi,)) + > 2*nu*xi*Subs(Derivative(f(_xi_1), _xi_1), (_xi_1,), (xi,)) - 2*nu*f(xi) + > xi*f(xi)*Subs(Derivative(f(_xi_1), _xi_1), (_xi_1,), (xi,)) - > f(xi)**2)/(xi**3*(nu*t)**(3/2)) > [] > None > > Any help will be welcome. > > - Almog > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. For more options, visit https://groups.google.com/groups/opt_out.
