```Date: Feb 14, 2013 2:09 AM
Author: mathgroup
Subject: Re: Differencing two equations

and much more comprehensible than   f@@@Equal@@@, etc.etc.etc.jb-----Original Message----- From: Alexei BoulbitchSent: Wednesday, February 13, 2013 3:50 AMSubject: Re: Differencing two equationsDear community,I have seen in this thread a lot of nice approaches that I really admire, butwriting simply:eq2 = b == s;eq1 = a == r;eq1[[1]] - eq2[[1]] == eq1[[2]] - eq2[[2]]a - b == r - sis shorter.Have fun, Alexei> a==r> b==s> I'd like to get:> a-b == r-sHi.   Here are a few ideas.v={a==r,b==s};Equal@@Subtract@@@{v[[All,1]],v[[All,-1]]}a-b==r-sEqual@@Subtract@@@Transpose[List@@@v]a-b==r-s{*  I like Inner  *)Inner[Subtract,a==r,b==s,Equal]a-b==r-s// or...Inner[Subtract,v[[1]],v[[2]],Equal]a-b==r-s= = = = = = = = = =HTH   :>)=E2=80=A8Dana DeLouisMac & Mathematica 9=E2=80=A8= = = = = = = = = =On Sunday, February 10, 2013 3:35:06 AM UTC-5, G B wrote:> I'm brand new to Mathematica, so I apologize for the naive questions...>>>> I'm trying to figure out how to difference two equations.  Basically if I=have:>> a==r>> b==s>>>> I'd like to get:>> a-b == r-s>>>> What I'm getting is more like (a==r) - (b==s).  I'm not sure how that's a > useful result, but is there a function to do what I'm looking for?>>>> A quick search of the archives seem to bring up ways of doing this from > using transformation rules to swap heads to unlocking the Equals operator > and hacking its behavior.  I'd like to avoid doing that kind of rewiring > for a simple operation, and I'd like to keep the syntax clean.>>>> The Core Language documentation makes a big point of how everything is > basically a list with different heads.  In this case, what I'm trying to > do would work if it were treated as a list ({a,b}-{r,s} returns {a-b,r-s}) > but doesn't work under Equal.>>>> Thanks for any suggestions.Alexei BOULBITCH, Dr., habil.IEE S.A.ZAE Weiergewan,11, rue Edmond Reuter,L-5326 Contern, LUXEMBOURGOffice phone :  +352-2454-2566Office fax:       +352-2454-3566mobile phone:  +49 151 52 40 66 44e-mail: alexei.boulbitch@iee.lu
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