Re: Improving Genetic Programming Efficiency
- To: mathgroup at smc.vnet.net
- Subject: [mg43176] Re: [mg43156] Improving Genetic Programming Efficiency
- From: William K Reinholtz <kirk.reinholtz at jpl.nasa.gov>
- Date: Sat, 16 Aug 2003 02:53:57 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
This is usually done with one of the Hold forms, and ReleaseHold[] when
you're ready to let it evaluate.
Is your overall desire to prevent evaluation of any kind until you get
the expression into a context where a,b, etc are properly defined?
On Friday, Aug 15, 2003, at 01:27 US/Pacific, hacksaw wrote:
> Hi,
>
> I am writing a genetic programming package in Mathematica. I would like
> to be able to create a Mathematica expression and store it in a
> variable
> or a list. The problem is that Mathematica will do some internal
> rearranging to place the expression in a canonical form. Here is an
> example:
>
> In[1]:= y := Plus[Times[Power[b, 2], a], Times[c, b]]
>
> In[2]:= FullForm[y]
>
> Out[2]//FullForm= Plus[Times[a,Power[b,2]],Times[b,c]]
>
> Previous, people who have written genetic programming packages have
> gotten around this "feature" of Mathematica by defining their own
> function names. This prevents the expression from being evaluated. At
> the time they want to evaluate the expression they uses the
> ReplaceAll[]
> function to change the name of the function to a Mathematica function.
>
> In[3]:= y := myPlus[myTimes[myPower[b, 2], a], myTimes[c,b]]
>
> In[4]:= FullForm[y]
>
> Out[4]//FullForm= myPlus[myTimes[myPower[b,2], a],myTimes[c,b]]
>
> In[5]:= FullForm[ReplaceAll[y,{myPlus -> Plus, myTimes -> Times,
> myPower -> Power}]]
>
> Out[5]//FullForm= Plus[Times[a,Power[b,2]],Times[b,c]]
>
> My issue is that this is a lot of extra overhead. If I had 4000
> expressions, each with a 1000 functions, this would be 4,000,000
> ReplaceAll[] function calls to rewrite the names of the functions.
>
> Does anyone have any suggestions that might be more efficient.
>
> Thanks in advance,
> David
>