Re: algebraic ReplaceAll?
- To: mathgroup at smc.vnet.net
- Subject: [mg122288] Re: algebraic ReplaceAll?
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Sun, 23 Oct 2011 06:25:50 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <201110221006.GAA29609@smc.vnet.net>
Mathematica pattern matching is syntactical and based on the FullForm of
an expression. These full forms show that you are not going to get a
match:
In[15]:= FullForm[Hold[-x + w]]
Out[15]//FullForm= Hold[Plus[Times[-1,x],w]]
In[16]:= FullForm[x - w]
Out[16]//FullForm= Plus[Times[-1,w],x]
If you want to make algebraic replacements you have to use algebra, not
pattern matching. For example:
Last[PolynomialReduce[-x + w, w - x - y, {x, w, y}]]
y
Or, if you need something more powerful, perhaps look here
=
http://groups.google.com/group/comp.soft-sys.math.mathematica/browse_thread/thread/634a54e2e844837f/ddf3803cab4f3a5f?lnk=gst&q=replacementfunction#ddf3803cab4f3a5f
here
=
http://groups.google.com/group/comp.soft-sys.math.mathematica/browse_thread/thread/1397ca25b770b9af/59f63501668f7fbe?lnk=gst&q=replacementfunction#59f63501668f7fbe
and lots of other similar posts on this topic.
Andrzej Kozlowski
On 22 Oct 2011, at 12:06, Dushan Mitrovich wrote:
> Is there a way to get ReplaceAll to actalgebraically, so it recognizes
> the negative of a replaced quantity as well as the positive? For
> example, this works
> In: x-w /. x-w->y
> Out: y
>
> but these don't
> In: -x+w /. x-w->y
> w-x /. x-w->y
> Out: w-x
> w-x
>
> - Dushan
>
>
>
>
- References:
- algebraic ReplaceAll?
- From: Dushan Mitrovich <dushanm@spinn.net>
- algebraic ReplaceAll?