Hi all,
I'm using sympy 0.7.4.1, and I've come across an issue I don't quite
understand. If I do
from sympy import *
x,z,t = symbols('x, z, t')
psi = Function('psi')(x,z)
j1 = Derivative(psi,x) - Derivative(psi,z)
j1.subs(Derivative(psi,x), t)
I get what I expect, t - d psi/dx. However, if I do the same thing with a
second derivative with respect to z, I get the following:
j2 = Derivative(psi,x) - Derivative(psi,z,2)
j2.subs(Derivative(psi,x), t)
it returns t - d^2 t/dz^2. I expect it to return t - d^2 psi/dz^2. Can
anyone point me to anything I might be doing wrong? I've tried defining t
as a Function, rather than as a symbol (t = Function('t')(x,z)), but that
does the exact same thing. I've also tried writing the second derivative in
j2 as Derivative(psi,z,z), but that also does the same thing (which I would
expect).
I've found this behavior both on my computer with Python 3.3.2 and on the
sympy live shell on sympy.org, which is currently SymPy 0.7.4.1 (Python
2.7.5).
Any advice you could provide would be very helpful.
thanks,
Jeff
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