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MathGroup Archive 2004

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Re: Trouble with NDSolve Function

  • To: mathgroup at
  • Subject: [mg51072] Re: Trouble with NDSolve Function
  • From: terryf at (Terry)
  • Date: Sun, 3 Oct 2004 05:47:54 -0400 (EDT)
  • References: <57tm0o$>
  • Sender: owner-wri-mathgroup at

I was interested to see your 1996 Mathematica query  because I have a
similar problem in 2004.  I could not find any responses to your query
on the interent so I'm taking the liberty of sending this email to ask
if you managed to solve the problem and, if so, how?

Any feedback would be most welcome.

Terry Fairclough  

On 2 Dec 1996 04:30:16 GMT, Wayne Davis wrote:
>I have had some trouble getting the Mathematica NDSolve function to
>and solve problems containing certain types of conditionals in the
dif eq,
>even though the problem seems properly stated to me. I am attaching
>example and would like to know what I'm doing wrong. (It appears that
>assignments don't get substituted into the conditional terms so that
>NDSolve can handle them as numerical values).
>q[i_]=If[y[i-1][t]>ya,q[i-1],k (y[i-1][t]-y[i][t])];
>difeqs=Table[c y[i]'[t]==q[i]-q[i+1],{i,1,imax}];
>   Differential equation does not evaluate to a number at
>    t = 0..
>{{y[1] -> InterpolatingFunction[{0., 0.}, <>],
>   y[2] -> InterpolatingFunction[{0., 0.}, <>],
>   y[3] -> InterpolatingFunction[{0., 0.}, <>]}}
>Thanks in advance for any help.
>Don Paddleford
>Westinghouse Savannah River Company
>Wayne Davis                 Q:  What has four legs and one arm?
>wdavis at          A:  A happy Pit Bull

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