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  • Christopher Subich's avatar
    Simplified tridiangonal solve algorithm; timing extensions · 3581d1c1
    Christopher Subich authored
    First and most trivially, this change adds a few more timing push/pop
    invocations relating to multigrid and especially to some of the MPI
    synchronization steps that might cause processors to wait on each other.
    More substantively, this change also adds a new tridiangonal solver
    based on the bog-standard forwards/backwards elimination Thompson
    algorithm (see Wikipedia).  This should be acceptable because the 1D
    problems being solved themselves come from a 2D problem, so we don't
    expect ill-conditioning; calling out to the GMRES banded solver was
    surprisingly a computational bottleneck perhaps because of pivoting.
    This change seems to decrease the line-solve time by about 80%, which in
    turn decreases the overall runtime (tank_rho test case) by 40%.