On Jun 13, 2010, at 11:25 AM, Alan Bromborsky wrote:
> Aaron S. Meurer wrote:
>> Wouldn't you just use the .subs() method, or does that not work?
>>
>> Aaron Meurer
>> On Jun 13, 2010, at 6:57 AM, Alan Bromborsky wrote:
>>
>>
>>> How would I do the following:
>>>
>>> I have a generic function: d_1 = Function('d_1')(x)
>>>
>>> that I apply to another function f in an expression such as y =
>>> 5*x_1**2+d_1(f).
>>>
>>> Later I wish to substitute an explicit function such as
>>>
>>> def D_1(f):
>>> return(diff(f,x_1))
>>>
>>> for d_1 and have y expanded after the substitution. For example if f =
>>> x_1**2+x_2**2 then
>>> y = 5*x_1**2+2*x_1
>>>
>>>
>>>
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>>>
>>
>>
> I tried this:
>
> from sympy import *
>
> x = Symbol('x')
> x_1 = Symbol('x_1')
> x_2 = Symbol('x_2')
>
> def df_1(F):
> global x_1
> return(diff(F,x_1))
>
>
> if __name__ == '__main__':
>
> F = Function('df')(x)
>
> y = x_1**2+x_2**2
>
> z = y+F(y)
>
> print z
>
>
> and got:
>
> Traceback (most recent call last):
> File "testtensor.py", line 26, in <module>
> z = y+F(y)
> File
> "/usr/local/lib/python2.6/dist-packages/sympy-0.6.7_git-py2.6.egg/sympy/core/basic.py",
> line 1310, in __call__
> raise TypeError("argument must be a dictionary")
> TypeError: argument must be a dictionary
>
> I must be missing something. I haven't even tried to substitute yet.
What are you trying to do with F(y)? You have df is a Function and F = df(x),
and you are trying to apply the function twice, df(x)(y), which is not allowed.
I think maybe you really mean to just have F = Function('df').
Aaron Meurer
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