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 Author Comment/Response John 08/31/05 10:14pm Hello, I get the following error message when I include the conditional into my definition for function f[a_}: Invalid integration variable or limit(s). Without this conditonal statement, x[1] equals a negative number, which is not realistic. The smallest number x[t] can equal is 0. I believe the error message is because x[t] takes on a constant numerical value due to the conditional statement and it forms the d(x[t]) part of the integral. Do you have any suggestions to get around this? If x[t]<=0.0001, I would like x'[t]=0 and y'[t]=-2*a*y[t]. Here are my equations: f[a_]:=NDSolve[{x'[t]==If[x[t]<=0.0001,0,-1.86* (1-y[t])*Integrate[x[t]^(2/3),{x[t],0,1}], y'[t]==If[x[t]<=0.0001,-2*a*y[t],-x'[t]-2*a*y[t], x[0]==1,y[0]==0},{x,y},{t,0,1}, Method->StiffnessSwitching] f[10] Thank you URL: ,

 Subject (listing for 'Invalid integration variable or limit(s)') Author Date Posted Invalid integration variable or limit(s) John 08/31/05 10:14pm Re: Invalid integration variable or limit(s) yehuda ben-s... 09/01/05 06:37am
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