Re: Reduce an expression into a given form.
- To: mathgroup at smc.vnet.net
- Subject: [mg130914] Re: Reduce an expression into a given form.
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Sat, 25 May 2013 05:38:39 -0400 (EDT)
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- Delivered-to: l-mathgroup@wolfram.com
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On 5/24/13 at 6:26 AM, francesco.cordoni88 at gmail.com (Francesco Cordoni) wrote: >I have an expression of the form N[a,b,c]/D[a,b,c] with a, b and c >some parameters on which N and D depend. I have to transform it into >something like A[a,b]/c with A that does not depend on c. Is there >any function in Mathematica that can do that? Thanks a lot for any >help. No in that you cannot use N and D as you attempt to do above. These have built-in meaning and if you paste N[a,b,c] into a notebook with default settings you will see the last comma and c are colored red indicating a syntax error. And D[a, b, c] gets evaluated to zero. It is impossible to say anything meaningful beyond the remarks above until you define your functions. Note, I can always do something like: In[6]:= n[a, b, c]/d[a, b, c] /. {n[x_, y_, _] -> k[x, y], d[_, _, x_] -> x} Out[6]= k[a, b]/c But since this type of replacement is akin to replacing characters in a string and is not doing any mathematics, it cannot be guaranteed to have any mathematical validity. And in fact since the functions n,d and k are undefined, the result is meaningless.