[petsc-users] Monotonic convergence in FGMRES.

[Vijay S. Mahadevan]

Hi all,

I am running a linear problem discretized with FEM on a diffusion
reaction system, with discontinuous source distribution. When I run
FGMRes with geometric multigrid as its preconditioner, I notice that
every time after the restart in fgmres, the new residual is orders of
magnitude higher than the previous iteration. I might be wrong on this
but should the restart not preserve monotonicity in convergence ? Or
am I thinking of a different variant of Gmres here. Here's the
residual norm as a function of iteration with number of restarts=50.

 40 KSP Residual norm 2.489810374358e-06
 41 KSP Residual norm 1.585813670005e-06
 42 KSP Residual norm 1.059211836025e-06
 43 KSP Residual norm 6.701461059247e-07
 44 KSP Residual norm 4.127634824940e-07
 45 KSP Residual norm 2.511364148934e-07
 46 KSP Residual norm 1.307034672896e-07
 47 KSP Residual norm 7.105770015635e-08
 48 KSP Residual norm 4.098578230710e-08
 49 KSP Residual norm 2.426160176080e-08
-------------------------------------------------------------------------
 50 KSP Residual norm 1.864914790828e+02
 51 KSP Residual norm 6.741080961009e+01
 52 KSP Residual norm 5.191621875736e+01
 53 KSP Residual norm 4.513782866249e+01
 54 KSP Residual norm 3.320195603375e+01
 55 KSP Residual norm 2.699941296855e+01
 56 KSP Residual norm 1.707998091297e+01
 57 KSP Residual norm 1.219599670348e+01

Any suggestions to obtain a more smoother convergence would be much
appreciated. Thank you,

Vijay