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 Boulbitch
Sent: Wednesday, February 13, 2013 3:50 AM
Subject: 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,
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Office phone : +352-2454-2566
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