On Dec 11, 2007 7:06 PM, Kirill Smelkov <[EMAIL PROTECTED]> wrote:
>
> Suresh,
>
> On Tue, Dec 11, 2007 at 09:47:58AM -0800, Suresh Jeevanandam wrote:
> >
> > Dear all,
> >
> > Let's say I have an expression:
> > 1/(a+b)
> >
> > I want to be able to simplify this to 1/a if we know that a is much,
> > much greater than b. Is there a way to achieve this already in sympy.
> > If not, I think this would be a nice feature for engineering people
> > who would always be making some approximations and get intuitions from
> > the simplified expressions :)
>
> An example related to your question:
>
> In [2]: e = 1/(x+y)
>
> In [3]: e
> Out[3]:
> 1
> -----
> x + y
>
> In [4]: e.series(y, 1)
> Out[4]:
> 1
> - + O(y)
> x
>
>
> You can do it more carefully:
>
> if y << x <==> t = y/x << 1, so
>
> In [5]: t = Symbol('t')
>
> In [6]: et = e.subs(y, t*x)
>
> In [7]: et
> Out[7]:
> 1
> -------
> x + t*x
>
> In [8]: ets = et.series(t, 1)
>
> In [9]: ets
> Out[9]:
> 1
> - + O(t)
> x
>
> In [10]: ets.subs(t, y/x)
> Out[10]:
> 1
> - + O(y/x, x, y)
> x
>
>
> Is that what you need?
Thanks Kirill, yes, that's the way to do it. And then, when
assumptions are implemented, we could just call a simple function to
simplify:
> 1
> - + O(y/x, x, y)
> x
to
> 1
> -
> x
Ondrej
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