Problems
Commonly encountered problems
- Singularity during integration (IFAIL nonzero) often means
either the equations are singular for your chosen parameter
set, or you are using an inappropriate method, or else you
are asking for a precision-level that cannot be achieved.
In such cases you should inspect the w_deqsol.txt and
iterate.txt files, or nagifail.txt if using the NAG library.
- Slow integration suggests you may be using a wrong method.
The BDF method is faster with a supplied Jacobian but,
if this is not happening, your Jacobian is probably wrong.
- Curve fitting is always slow but, if it takes much longer
than the test files, you are probably using poor starting
estimates.
- Curve fitting leading to a very poor or strange looking fit
is usually caused by one or more of the following.
- You are not using a correct set of differential equations.
- The differential equations are not formulated correctly.
- You have senseless initial condition/parameter-estimates.
- You are not using the right method or control parameters.
- You are not using the correct transformation matrix A.
- The integration procedure cannot function correctly causing
an exit with the initial parameters unchanged.
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