Hi, On Fri, Apr 03, 2009 at 08:41:05AM -0700, Colin Gillespie wrote: > > Dear All, > > Quick question. I have a polynomial: > > p =Poly(2*x*y+y, x, y) > > and I want to substitute in y = y+5 and x= x+1 How would I do this? > > I've tried things like: > > p.subs((y, y+5), (x, x+1)) > > but this doesn't work. > > Cheers > > Colin >
you should refer to Basic.subs() docstring:
In [1]: p = Poly(2*x*y+y, x, y)
In [2]: p.subs?
Type: instancemethod
Base Class: <type 'instancemethod'>
String Form: <bound method Poly.subs of Poly(2*x*y + y, x, y)>
Namespace: Interactive
File: /home/matt/repo/git/sympy/sympy/core/basic.py
Definition: p.subs(self, *args)
Docstring:
Substitutes an expression.
Calls either _subs_old_new, _subs_dict or _subs_list depending
if you give it two arguments (old, new), a dictionary or a list.
Examples:
>>> from sympy import *
>>> x,y = symbols('xy')
>>> (1+x*y).subs(x, pi)
1 + pi*y
>>> (1+x*y).subs({x:pi, y:2})
1 + 2*pi
>>> (1+x*y).subs([(x,pi), (y,2)])
1 + 2*pi
In [3]: p.subs({y:y+5,x:x+1})
Out[3]: Poly(2*x*y + 10*x + 3*y + 15, x, y)
In [4]: p.subs([(y, y+5), (x, x+1)])
Out[4]: Poly(2*x*y + 10*x + 3*y + 15, x, y)
In [5]: p.as_basic().subs({y:y+5,x:x+1})
Out[5]: 5 + y + 2⋅(1 + x)⋅(5 + y)
In [6]: expand(_) == _4.as_basic()
Out[6]: True
--
Mateusz
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