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    Benoit Bovy
    @benbovy
    Hello!
    rbrtmch
    @rbrtmch
    Hi Benoit et al, quick question. What type of a boundary condition does the (fortran) flexure subroutine use? -- Rob Moucha
    Benoit Bovy
    @benbovy
    Hi Rob, welcome! The flexure subroutine should use the boundary condition set with the Fastscape_Set_BC subroutine (https://fastscape.org/fastscapelib-fortran/#_fastscape_set_bc). Note that a bug has been fixed recently regarding this (https://github.com/fastscape-lem/fastscapelib-fortran/pull/34). It should work as expected using the last release 2.8.2.
    rbrtmch
    @rbrtmch
    Thanks for the quick reply Benoit. So the fixed condition would be equivalent to a clamped and cyclic to periodic wrap-around as defined in Wickert (2016) gFlex paper www.researchgate.net/figure/Schematics-of-boundary-condition-types-allowed-in-the-finite-difference-solutions-to_fig3_297737148
    Benoit Bovy
    @benbovy
    Yes I think so, but I'm not 100% sure. Jean Braun implemented and maintain this implementation so he could confirm.
    rbrtmch
    @rbrtmch
    Hi @benbovy, in our application we found that the 100 Gauss-Seidel iterations was not enough for precipitation that was less than 0.6 m/yr. We also tested this with the mountain example. When increased to 200, the loops converged. We came across this because we are varying the precipitation from arid to humid cyclically in our models. Perhaps a future feature request would be to allow for the user to be able to set this if desired.
    Benoit Bovy
    @benbovy
    Hi Rob, yes I agree this max number of iterations should be configurable by the user. I opened fastscape-lem/fastscapelib-fortran#40. Thanks for reporting and for the description of your use case!
    rbrtmch
    @rbrtmch
    Hi Benoit, we found that the Gauss Seidel iterations does not converge for precipitation less than 0.6 m/yr. We tried this also with the mountain example. Any thoughts? Could it be that precipitation is just to low to cause incision?
    I should add that we increased the iterations all the way up to 299.
    Benoit Bovy
    @benbovy
    Hi Rob, which value do you use for g (bedrock dimensionless deposition/transport coefficient)? For g > 1 the number of iterations may grow rapidly, which is a limitation of the implicit numerical scheme used to solve the equation. Setting lower precipitation values (which thus impact the values of "drainage area") may amplify this effect (because of the G / A ratio in the PDE solved by fastscapelib-fortran).
    rbrtmch
    @rbrtmch
    We used g=1 .