On May 4, 2010, at 4:25 AM, Sebastian wrote:
> On 05/04/2010 10:32 AM, janwillem wrote:
>> I need some explanation on the workings of SymPy. As an example the
>> following script:
>> import sympy
>> X, F, B = sympy.symbols('XFB')
>> Y = X / F - B #eqn 1
>> DY = sympy.Matrix(sympy.diff(Y, (X, F, B))).T
>>
> Do sympy.diff(Y, (X, F, B), evaluate=True) instead for now. But you're
> right - this shouldn't be necessary. Somehow the vectorization of the
> diff method seems to fail and set evaluate to False.
I created issue 1929 for this.
Aaron Meurer
>> print DY
>>
>> I had expected (eqn 2): [1/F, -X/F**2, -1]
>> But get: [D(-B + X/F, X), D(-B + X/F, F), D(-B + X/F, B)]
>>
>> Not after doing a trick of which I cannot remember why I tried it, I
>> get the desired result
>> DY = DY.subs({X:X, F:F, B:B})
>>
> This works because subs evaluates the expression in the end (which
> wasn't done before).
>> From the doc I had thought that DY.doin() would work but that gives
>> "raise AttributeError()".
>>
> First, the name of the method is doit. Second, DY is a python tuple
> which doesn't have this method.
>> So there is obviously something I do not understand, please some help
>> Janwillem
>>
>>
> Sebastian
>
> --
> You received this message because you are subscribed to the Google Groups
> "sympy" group.
> To post to this group, send email to sy...@googlegroups.com.
> To unsubscribe from this group, send email to
> sympy+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/sympy?hl=en.
>
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To post to this group, send email to sy...@googlegroups.com.
To unsubscribe from this group, send email to
sympy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sympy?hl=en.
