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why strange solutions obtained?

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why strange solutions obtained?

a simple example, but got strange results. while matlab can give reasonable answers, but i dont like the matlab codes. see in attached

kinetics+odes.JPG

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Re: why strange solutions obtained?

Maybe it would help if you explain why you think that the result is wrong and what result (Matlab screenshot) you expect.

You want the system to be solved for a time interval up to 10^4 but you allow just (the default) 10^3 steps. A step width of 10 time units maybe is too large for a meaningful result. You may consider to solve for a smaller time interval and/or increase the number of iteration steps (thats an additional argument of odesolve).

I tried and the result is that A(t) goes down to zero right at the beginning when the precison is enhanced that way.

It looks like A is transferred amost immediatly to E, which is, looking at your coefficients k, no big surprise. Could it be a problem with numerical precision or what result did you expect? Your coefficients are rather big and k3 and k5 seem to be nearly neglectable compared to the others. Are you sure you used the same equations and the same coefficients in Matlab?

1.png

Can it be that it should be

2.png

3.png

View solution in original post

3 REPLIES 3

Re: why strange solutions obtained?

Maybe it would help if you explain why you think that the result is wrong and what result (Matlab screenshot) you expect.

You want the system to be solved for a time interval up to 10^4 but you allow just (the default) 10^3 steps. A step width of 10 time units maybe is too large for a meaningful result. You may consider to solve for a smaller time interval and/or increase the number of iteration steps (thats an additional argument of odesolve).

I tried and the result is that A(t) goes down to zero right at the beginning when the precison is enhanced that way.

It looks like A is transferred amost immediatly to E, which is, looking at your coefficients k, no big surprise. Could it be a problem with numerical precision or what result did you expect? Your coefficients are rather big and k3 and k5 seem to be nearly neglectable compared to the others. Are you sure you used the same equations and the same coefficients in Matlab?

1.png

Can it be that it should be

2.png

3.png

View solution in original post

Re: why strange solutions obtained?

Thank u very much for the explainations!

The keyponit lies in the negative symbol before activie energy.

Re: why strange solutions obtained?

Fan CG wrote:

Thank u very much for the explainations!

The keyponit lies in the negative symbol before activie energy.

Yes, Werner is one "minus guru"

See please http://communities.ptc.com/message/260444

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