Re: new function
- To: mathgroup at smc.vnet.net
- Subject: [mg67305] Re: new function
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Sat, 17 Jun 2006 04:36:28 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 6/16/06 at 12:27 AM, gianfred at le.infn.it wrote:
>I'm writing a package and I want to define a function of the
>form: Function[a_,{list_}], where "a" is a generic expression of
>more variables and "list" is a list of those variable that must go
>to zero. So in this way, Function automatically eliminate the
>variables that I specify after the comma. How can I create this
>function?
If it is acceptable to literally substitute zero for each of the variables this is quite simple. For example, the following will do the trick
zeroVars[a_, varList_]:=a/.Thread[varList->0]
For an arbitrary polynomial
poly = 10*z^3 + 14*z^2 + 2*z + 19*x^2 + y + 11;
In[19]:=
zeroVars[poly,{x,z}]
Out[19]=
y+11
or
In[20]:=
zeroVars[poly,{y,z}]
Out[20]=
19 x^2 + 11
But note in general simply substituting 0 for the variables will not give useful results. For example, if the expression contained Sin[x]/x and x were the variable to be "zeroed" you would get an indeterminate result from this simple substitution
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