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# Two Problems with NDSolve, Overflow and Projection method

Posted 10 years ago
 Hello I tried to solve a system first order differential equations together with a constraint equation. I use the Method->Projection to check if the constraint holds at each step. However, two problems occur: The messages: General::ovfl: Overflow occurred in computation. and General::unfl: Underflow occurred in computation,  appear and I do not how to handle them. The second problem occurs by the message: NDSolve::nlnum: "The function value {Overflow[],Overflow[],Overflow[],Overflow[]} is not a list of numbers with dimensions {4} at {t,u[t],x[t],y[t],z[t]}...  I have attached the image of the code with the given explanations in (**) for convenience. I would appreciate if any one give me a help. My best regards Hadi Attachments:
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Posted 10 years ago
 Replace ... \[Theta]=0.182; w=0; \[Rho]i=4.2; xi=0.0; ui=8.71; adot= -6.4; zi=26.57; om=11.72; ti=0.0; ts=10000; ... g = NDSolve[..., WorkingPrecision -> MachinePrecision] with ... \[Theta]=182/1000;w=0; \[Rho]i=42/10;xi=0;ui=871/100;adot= -64/10;zi=2657/100;om=1172/100;ti=0;ts=10000; ... g = NDSolve[..., WorkingPrecision -> 64] Plot[{x[t], x'[t], x''[t]} /. g[[1]], {t, 0, 29.16}] Plot[{u[t], u'[t], y[t]} /. g[[1]], {t, 0, 29.16}] Plot[{z[t]} /. g[[1]], {t, 0, 29.16}] and the overflow problems are no longer reported, but NDSolve::ndsz: At t == 29.1681...864., step size is effectively zero; singularity or stiff system suspected. >> `remains.
Posted 10 years ago