Sorry the title in the FAQ is a bit tongue-in-check. http://www.mcs.anl.gov/petsc/documentation/faq.html#functionjacobian
> On Dec 9, 2016, at 12:45 PM, Derek Gaston <[email protected]> wrote: > > Is there a way to tell SNES to simultaneously compute both the residual and > the Jacobian in one callback? > > My code can compute both simultaneously and it will be more efficient (think > FE where you can reuse the shape-functions, variables, material properties, > etc. for both residual and Jacobian computation). In addition, I also have > automatic differentiation as an option which _definitely_ computes both > efficiently (and actually computes residuals, by themselves, much slower). > > I was thinking that I may just save off the Jacobian whenever the initial > residual computation is asked for by SNES... and then just return that > Jacobian when SNES asks for it. This may be a bit dicey though as SNES can > ask for residual computations at many different points during the solve. > > Thanks for any help! > > Derek
