Thanks Aaron,
To my needs,
import sympy
import math
diff(sympy.sin(x)*diff(u(x),x),x)
is a good choice because math functions are used in other places.
I will try this.
czbebe
On 1月6日, 午後12:11, "Aaron S. Meurer" <[email protected]> wrote:
> 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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