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Re: Modifying equations


eqn1=a==b;
eqn2=c==d;

Thread[eqn1+eqn2, Equal]

a + c == b + d

Off[Sum::itform];
combSum=Sum[x_,iter_]+Sum[y_,iter_]:>Sum[x+y,iter];
On[Sum::itform];

Sum[a[i],{i,0,n}]+Sum[b[i],{i,0,n}]/.combSum

Sum[a[i] + b[i], {i, 0, n}]


Bob Hanlon

> 
> From: "Kalle Rutanen" <kalle_rutanen at nospam.hotmail.com>
To: mathgroup at smc.vnet.net
> Date: 2005/07/30 Sat AM 01:25:07 EDT
> Subject: [mg59167] [mg59135] Modifying equations
> 
> Hello
> 
> My intention is to write a mathematical paper which derives results step by
> step. So here is my first question:
> 
> Given the equations
> eqn1 = a == b
> eqn2 = c == d
> 
> How can I combine these to form (for example)
> a + c == b + d ?
> 
> I tried the obvious eqn1 + eqn2, but that does not seem to work...
> 
> Second question:
> 
> Given this:
> Sum[a_i, {i, 0, n}] + Sum[b_i, {i, 0, n}]
> How can I make Mathematica combine the sums giving:
> Sum[a_i + b_i, {i, 0, n}] ?
> 
> Thanks.
> 
> 
> 


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