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A problem with NDSolve

Posted 9 years ago

I attached my program. It is a problem of solving 6 third-order ODEs with 18 boundary conditions. After using NDSolve to get the numerical solutions of the problem, I plotted the first and second derivatives. I believe that the graphs of the first and second derivatives are wrong, since they are totally different from what I expected. Besides, in the boundary conditions, there is one stipulating that u2a''[1/2]==0. But after I extracted the results, I got u2a''[1/2]==-0.614559. So there is definitely something wrong, either with my code or with the algorithm of NDSolve. I don't know where the problem is. Could anyone help me? Many thanks!!

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POSTED BY: Hui Sun
4 Replies

This is a boundary value problem, not a initial value problem. Actually, function u2a[x] is defined on 1/2=<x<=1, and u6b[x] is defined on 1=<x<=3/2, so there cannot be u2a'[0] and u6b[0]. I don't think there is anything wrong with my boundary conditions, since I wrote them according to the basic principles of mechanics, although I could not guarantee that they are 100% correct. Anyway, many thanks for your reply and help!

POSTED BY: Hui Sun

I used "method of Lines" and it helped.I found a website that can help you solve the problem.I hope. LINK

See file Attachment.

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POSTED BY: Mariusz Iwaniuk

Many thanks for your help! After thinking it over, I feel that maybe I did give some wrong boundary conditions...Sorry for the time you spend on this problem...Once again, many thanks.

POSTED BY: Hui Sun

u2b'[0] = 0 and u2b'[1/2] = u2a'[1/2] Here is a mistake. Initial condition he can not have two values and forgot u6b[?]==?.

enter image description here so u2b'[0] = 0 ,u2b'[0] = u2a'[0] and e.g u6b[0]=0

POSTED BY: Mariusz Iwaniuk
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