"Zhang, Hong" <[email protected]> writes: >> On Oct 20, 2017, at 3:15 PM, Jed Brown <[email protected]> wrote: >> >> "Zhang, Hong" <[email protected]> writes: >> >>> Another confusion which is not related to this topic is the usage of the >>> word "DAE". >>> I disagree with the statement "In general, this (the general form) is a >>> differential algebraic equation (DAE)" on page 141 of the manual. >>> The word "DAE" has been abused in the comments of many TS functions >>> (including TSComputeIFunction), where it actually should mean "DAE or ODE". >>> PETSc uses the same interfaces for both DAE and ODE, but it is wrong to >>> consider ODE as a special case of DAE. >>> They are fundamentally different from each other and should be >>> distinguished explicitly in the manual and the source code. >> >> Is this not valid usage? >> >> "Thus, ODEs have index 0." > > One can think of scalar as 0d matrix. But how often do people use 0d matrix > for scalar?
The elegance of differential geometry would be lost if scalars were not 0-forms. > When people say DAE, naturally it refers to DAE with index 1 or higher > (ODE+algebraic constraints). > If PETSc TS developers are really DAE zealots, at least it should be > specified that their "DAE" includes index 0 DAE. I'm fine with explicitly stating that ODE are index 0 DAE and having phrases like "if your DAE is an ODE, the explicit interface can be used".
