Re: Differencing two equations

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• Subject: [mg129792] Re: Differencing two equations
• From: "mathgroup " <fizzymath at knology.net>
• Date: Thu, 14 Feb 2013 02:09:18 -0500 (EST)
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and much more comprehensible than   f@@@Equal@@@, etc.etc.etc.

jb

-----Original Message-----
From: Alexei Boulbitch
Sent: Wednesday, February 13, 2013 3:50 AM
To: mathgroup at smc.vnet.net
Subject: [mg129792] Re: Differencing two equations

Dear community,

I have seen in this thread a lot of nice approaches that I really admire,
but
writing simply:

eq2 = b == s;
eq1 = a == r;

eq1[[1]] - eq2[[1]] == eq1[[2]] - eq2[[2]]

a - b == r - s

is shorter.

Have fun, Alexei

> a==r
> b==s

> I'd like to get:
> a-b == r-s

Hi.   Here are a few ideas.

v={a==r,b==s};

Equal@@Subtract@@@{v[[All,1]],v[[All,-1]]}
a-b==r-s

Equal@@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 DeLouis
Mac & 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, LUXEMBOURG

Office phone :  +352-2454-2566
Office fax:       +352-2454-3566
mobile phone:  +49 151 52 40 66 44

e-mail: alexei.boulbitch at iee.lu

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