Actually, that's what I was already trying:
import sympy
%load_ext sympy.interactive.ipythonprinting
x,x0 = sympy.var(('x','x0'))
f=sympy.Function('f') (x)
sympy.Subs(sympy.diff(f, x), x, x0)
That just gives (in an IPython notebook):
Subs(Derivative(f(x), x), (x,), (x0,))
which is strange because the ASCII and latex versions work as you say.
Am I doing something wrong?
-David
On Wed, Jan 23, 2013 at 7:50 AM, Aaron Meurer <[email protected]> wrote:
> It does. What you have is the string form, which is designed to be
> readable, but also copy-pastable. Like almost all SymPy objects, there
> are pretty printers for Subs, including ASCII, Unicode, and LaTeX.
> For ASCII/Unicode, you get the bar notation:
>
> In [3]: pprint(Subs(diff(f(x), x), x, 0))
> ⎛d ⎞│
> ⎜──(f(x))⎟│
> ⎝dx ⎠│x=0
>
> In LaTeX, you get
>
> In [1]: latex(Subs(f(x), x, 0))
> Out[1]: \left. \operatorname{f}{\left (x \right )} \right|_{\substack{ x=0
> }}
>
> which is the same thing. If you want this in the IPython notebook,
> just use the SymPy printing extension, which will make everything
> print with LaTeX using MathJax. Just run
>
> %load_ext sympy.interactive.ipythonprinting
>
> at the top of the notebook (init_printing(use_latex=True) should work too).
>
> Aaron Meurer
>
> On Sat, Jan 19, 2013 at 10:00 AM, David Ketcheson <[email protected]>
> wrote:
> > Thanks, Aaron. That works, though I had hoped for something prettier
> than:
> >
> > Subs(Derivative(f(_x), _x), (_x,), (x0,))
> >
> > It would be really great if sympy knew how to print this kind of thing
> > nicely (say, in an IPython notebook).
> >
> > -David
> >
> > On Wed, Jan 16, 2013 at 9:25 PM, Aaron Meurer <[email protected]>
> wrote:
> >>
> >> Try Subs(diff(f, x), x, x0).
> >>
> >> Note that mathematically, this should be the same as diff(f,
> >> x).subs(x, x0), because x is a bound (not free) variable in this
> >> expression, it doesn't matter if a different one is used, or if an
> >> expression is used that doesn't use it at all. Note that if you use a
> >> non-variable instead of x0, it will automatically give you the Subs
> >> form (in particular, if you use a number, like diff(f, x).subs(x,
> >> 10)). It will also give you the Subs form if you later substitute x0
> >> for a number (in terms of x0, but it doesn't matter because x0 serves
> >> as a dummy variable in this case).
> >>
> >> Aaron Meurer
> >>
> >> On Wed, Jan 16, 2013 at 5:06 AM, David Ketcheson <[email protected]>
> wrote:
> >> > Is there any way in sympy to express the derivative of an abstract
> >> > function
> >> > evaluated at a point? I can do
> >> >
> >> > import sympy
> >> > x,x0 = sympy.var(('x','x0'))
> >> > f=sympy.Function('f') (x)
> >> > sympy.diff(f)
> >> >
> >> > to get the derivative w.r.t. x evaluated at x. If I do
> >> >
> >> > sympy.diff(f).subs(x,x0)
> >> >
> >> > then I get the derivative w.r.t. x0 evaluated at x0. Can I get the
> >> > derivative w.r.t. x evaluated at x0?
> >> >
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