Suggestion: update spde stuff with functions from fmesher package

[williamaeberhard]

Hi Kasper,
Just a suggestion about dependencies: some parts of RTMB/tmb_examples/spde.R rely on functions in the R package INLA such as inla.spde2.matern and inla.mesh.2d. This is the case for instance for the inla_spde object in RTMB/tmb_examples/spde_mesh.RData which goes back to adcomp/tmb_examples/spde_mesh.R. I may be wrong, but I think some of these INLA functions are not much in development anymore, and their equivalent in the R package fmesher should be favored in the long run. Notably fmesher::fm_mesh_2d could replace INLA::inla.mesh.2d and fmesher::fm_fem could replace inla.spde2.matern, where for the latter $c0, $g1, and $g2 are the equivalent of $M0, $M1, and $M2, respectively.
Cheers,
William

[skaug]

I agree, and I will see if I can fix it.