What's the result that you would expect? I get
In [31]: diff(F_tensor, b)
Out[31]: -2⋅(-a - b⋅x[i] + y[i])⋅x[i]
By the way, your code should just be i = Idx('i'). map returns a list in
Python 2 and an iterator in Python 3.
Aaron Meurer
On Fri, Aug 8, 2014 at 1:46 PM, Станислав Иванов <[email protected]>
wrote:
> >>> from __future__ import division ... ... from sympy import * ... from
> sympy.tensor import IndexedBase, Idx ... ... a, b = symbols('a b') ...
> F_tensor = symbols('F_tensor', cls=Function)
> ... ... i = map(Idx, ['i']) ... ... x = IndexedBase('x') ... y =
> IndexedBase('y') ...
> >>> F_tensor = (y[i] - (b*x[i]+a))**2
> >>> F_tensor
> (−a−bx[i]+y[i])2
> >>> diff(F_tensor, b)
> −2(−a−bx[i]+y[i])2 x[i](−a−bx[i]+y[i])−1
>
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