#spectralsolver polarisation
spectralderivative fwbw_difference
err_div_tolrel  1e-3
itmin 2
petsc_options -mech_snes_type anderson -mech_snes_anderson_beta 1.0 -mech_snes_anderson_restart 10 -thermal_snes_type anderson -thermal_snes_anderson_beta 1.0