Re: rules->function
- To: mathgroup at smc.vnet.net
- Subject: [mg7404] Re: [mg7338] rules->function
- From: seanross at worldnet.att.net
- Date: Fri, 30 May 1997 01:20:25 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Lord of Darkness wrote:
>
> Hello All,
>
> If I solve a set of simultaneous equations and get a simple answer like
> zrule = z-> x^2 + y^2
>
> but I then want to evaluate
> fn[x_,y_] := z + some more stuff.....
>
> I tried saying
>
> fn[x_,y_] := Replace[z,zrule] + ....
>
> but it doesn't seem to handle it the way I wanted...
>
> Is there a correct way of doing this ?
>
> thanks
>
> John B
No, there is no single correct way to do it. My particular way is like
this:
f[a_,b_]=Evaluate[z/.zrule]/.{x->a,y->b}
The reason your approach did not work is that mathematica has real
trouble when function arguments appear on the left hand side of
replacement rules. You also used := which waits to execute the
instructions until called upon. By that time, x and y are numbers, not
generic symbols and that gets you into trouble as well.
P.S. Whats with the "Lord of Darkness" handle? Were you Darth Vader in
a previous life?