Thanks Ondrej,
>I strongly suggest not to use this string syntax
I am sorry, but I want to get the derivatives of general equation
including some functions, exp, sin/cos/tan, and pow and so on.
It is given by a string variable.
import sympy
x = sympy.symbols('x')
f = pow(x,2)
g = sympy.diff(f,x)
print g
This gives 2*x and is correct, but f = pow(x,2) seems questionable.
You said "no "pow" function in sympy", but g1= sympy.diff(pow(x,2),x)
gives correct result 2*x. Why ?
Pow function is critical for me because my mathml converter gives
pow functions even if simple x**2 is converted to pow(x,2).
czbebe
On 12月8日, 午前11:25, Ondrej Certik <ond...@certik.cz> wrote:
> On Mon, Dec 7, 2009 at 5:57 PM, czbebe <o...@bpe.es.osaka-u.ac.jp> wrote:
> > Hi,
>
> > Following porblem I met.
>
> > import sympy
> > x = sympy.symbols('x')
> > f = 'pow(x,2)'
> > g = sympy.diff(f,x)
> > print g
> > g1= sympy.diff(pow(x,2),x)
> > print g1
>
> > g outputs D(pow(x, 2), x)
> > g1 is 2*x
>
> > g1 is all right, but g is wrong.
>
> > if f='sin(x)', g =con(x) and it is correct.
>
> > Why f = 'pow(x,2)' can't give correct answer ?
>
> That's because there is no "pow" function in sympy, so sympify just
> creates an unknown function "pow" for you:
>
> In [1]: p = sympify("pow(x, 2)")
>
> In [2]: p
> Out[2]: pow(x, 2)
>
> In [3]: p.diff(x)
> Out[3]:
> d
> ──(pow(x, 2))
> dx
>
> it's the same as using any other name, like this:
>
> In [4]: p = sympify("powx(x, 2)")
>
> In [5]: p
> Out[5]: powx(x, 2)
>
> What you want to use is "Pow", then it works.
>
> That being said, I strongly suggest not to use this string syntax at
> all (if there is some other way to do that), as you can see, it easily
> leads to confusion.
>
> Ondrej- 引用テキストを表示しない -
>
> - 引用テキストを表示 -
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