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RE: Coupled Differential Equations

  • To: mathgroup at
  • Subject: [mg34775] RE: [mg34751] Coupled Differential Equations
  • From: "Curt Fischer" <cfisher at>
  • Date: Thu, 6 Jun 2002 01:54:58 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Dear Cyrill,

You didn't give very many details of your problem.  Therefore I am
unsure if my answer will help you or not. 

>From: Cyrill Slezak [mailto:slezakcy at]
To: mathgroup at
>Subject: [mg34775] [mg34751] Coupled Differential Equations
>I understand that NDSolve will solve a set of first order coupled.
>Here is my problem: I have a set of 20+ equation that all have the
>same structure and I can't seem to find an easy way to input them. For
>any help I'd be highly appreciative.
>The equations are of the form
>d V_k(l)/d l = V_k(l) + Sum[ V_k'(l), (k not equal k')]
>where k is the number of diff. eqn.

Using the function Table[] is one way to do this:

In[1]:=	n = 20; 
		eqns = Table[\(v\_k'\)[l] == v\_k[l] + \ Sum[If[kp == k,
0, \(v\_kp'\)[l]], {kp, 1, n}], {k, 1, n}]

In[2]:=	vars = Table[v\_k[l], {k, 1, n}]

In[3]:=	DSolve[eqns, vars, l]

I used "kp" instead of your "k'".  Hope this helps you.

Curt Fischer
Dept. of Bioengineering
Tokyo Institute of Technology

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