Matthew Knepley <[email protected]> writes: > On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <[email protected]> wrote: > >> Can you elaborate a bit more on your problem? >> >> If your problem is an index-1 DAE, there is no need to use a projection >> method, and it is perfectly fine to set it up as a DAE in PETSc. For >> high-index DAEs, you may have to use TSSetPostStep() to implement your own >> projection algorithm. >> > > Please define index.
Think of it as a measure of singularity of the "mass matrix". Higher index DAE have more complicated constraints on compatibility of initial conditions. It's covered in any book or paper on DAEs.
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