[petsc-users] projection methods in TS

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <hongzhang at anl.gov> 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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