On Jan 5, 2010, at 7:32 PM, czbebe wrote:
> Dear members,
>
> import sympy
> import math
I believe the problem lies here. You are importing math, which imports the
math sin, which doesn't work with SymPy symbolic operations. You have some
options:
- Don't import math. If you need to evaluate a floating point expression, use
N() or .evalf(), as in sin(1.2).evalf(). If you need other things from math,
do explicit imports instead of import *. Actually, it's best to use explicit
imports anyway, especially if you are writing a script.
- If you really want math behavior, use lambdify(sin(x), x, "math").
- Do from math import sin as msin or some similar. That is, use the as
keyword.
- Don't import from. That is, just do import sympy and import math and then
use sympy.sin and so on. Doing import sympy as S can make this easier.
One of these should fit your needs. If not, I am sure someone else on this
list can come up with yet another solution.
Aaron Meurer
> u = Function('u')
> x = Symbol('x')
> diff(diff(u(x),x),x) = D(u(x), x, x) ii is all right.
> diff(x*diff(u(x),x),x) = x*D(u(x), x, x)+D(u(x), x) it is all right.
>
> diff(sin(x)*diff(u(x),x),x) gives an error.
>
> Can anyone show me the correct way to get a correct result ?
>
> czbebe
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