! Copyright 2011-13 Max-Planck-Institut für Eisenforschung GmbH
!
! This file is part of DAMASK,
! the Düsseldorf Advanced MAterial Simulation Kit.
!
! DAMASK is free software: you can redistribute it and/or modify
! it under the terms of the GNU General Public License as published by
! the Free Software Foundation, either version 3 of the License, or
! (at your option) any later version.
!
! DAMASK is distributed in the hope that it will be useful,
! but WITHOUT ANY WARRANTY; without even the implied warranty of
! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
! GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License
! along with DAMASK. If not, see <http://www.gnu.org/licenses/>.
!
!--------------------------------------------------------------------------------------------------
! $Id$
!--------------------------------------------------------------------------------------------------
!> @author Pratheek Shanthraj, Max-Planck-Institut für Eisenforschung GmbH
!> @author Martin Diehl, Max-Planck-Institut für Eisenforschung GmbH
!> @author Philip Eisenlohr, Max-Planck-Institut für Eisenforschung GmbH
!> @brief Polarisation scheme solver
!--------------------------------------------------------------------------------------------------
module DAMASK_spectral_solverPolarisation
 use prec, only: & 
   pInt, &
   pReal
 use math, only: &
   math_I3
 use DAMASK_spectral_utilities, only: &
   tSolutionState
 
 implicit none
 private
#include <finclude/petscsys.h>
#include <finclude/petscdmda.h>
#include <finclude/petscsnes.h>

 character (len=*), parameter, public :: &
   DAMASK_spectral_solverPolarisation_label = 'polarisation'
   
!--------------------------------------------------------------------------------------------------
! derived types 
 type tSolutionParams                                                                               !< @todo use here the type definition for a full loadcase including mask
   real(pReal), dimension(3,3) :: P_BC, rotation_BC
   real(pReal) :: timeinc
   real(pReal) :: timeincOld
   real(pReal) :: temperature
   real(pReal) :: density
 end type tSolutionParams
 
 type(tSolutionParams), private :: params
 real(pReal), private, dimension(3,3) :: mask_stress = 0.0_pReal

!--------------------------------------------------------------------------------------------------
! PETSc data
 DM,   private :: da
 SNES, private :: snes
 Vec,  private :: solution_vec
 
!--------------------------------------------------------------------------------------------------
! common pointwise data
 real(pReal), private, dimension(:,:,:,:,:), allocatable :: &
   F_lastInc, &                                                                                     !< field of previous compatible deformation gradients
   F_lastInc2, &                                                                                    !< field of 2nd previous compatible deformation gradients
   F_tau_lastInc, &                                                                                 !< field of previous incompatible deformation gradient 
   Fdot, &                                                                                          !< field of assumed rate of compatible deformation gradient
   F_tauDot                                                                                         !< field of assumed rate of incopatible deformation gradient
 complex(pReal),private, dimension(:,:,:,:,:), allocatable :: inertiaField_fourier

!--------------------------------------------------------------------------------------------------
! stress, stiffness and compliance average etc.
 real(pReal), private, dimension(3,3) :: &
   F_aimDot, &                                                                                      !< assumed rate of average deformation gradient
   F_aim = math_I3, &                                                                               !< current prescribed deformation gradient
   F_aim_lastInc = math_I3, &                                                                       !< previous average deformation gradient
   P_av = 0.0_pReal, &                                                                              !< average 1st Piola--Kirchhoff stress
   P_avLastEval = 0.0_pReal                                                                         !< average 1st Piola--Kirchhoff stress last call of CPFEM_general
   character(len=1024), private :: incInfo                                                          !< time and increment information
 real(pReal), private, dimension(3,3,3,3) :: &
   C_volAvg = 0.0_pReal, &                                                                          !< current volume average stiffness 
   C_volAvgLastInc = 0.0_pReal, &                                                                   !< previous volume average stiffness
   C_minMaxAvg = 0.0_pReal, &                                                                       !< current (min+max)/2 stiffness
   S = 0.0_pReal, &                                                                                 !< current compliance (filled up with zeros)
   C_scale = 0.0_pReal, &                             
   S_scale = 0.0_pReal
 
 real(pReal), private :: &
   err_stress, &                                                                                    !< deviation from stress BC
   err_curl, &                                                                                      !< RMS of curl of F
   err_div                                                                                          !< RMS of div of P
 logical, private :: ForwardData
 integer(pInt), private :: &
   totalIter = 0_pInt                                                                               !< total iteration in current increment
 
 public :: &
   Polarisation_init, &
   Polarisation_solution, &
   Polarisation_destroy
 external :: &
   VecDestroy, &
   DMDestroy, &
   DMDACreate3D, &
   DMCreateGlobalVector, &
   DMDASetLocalFunction, &
   PETScFinalize, &
   SNESDestroy, &
   SNESGetNumberFunctionEvals, &
   SNESGetIterationNumber, &
   SNESSolve, &
   SNESSetDM, &
   SNESGetConvergedReason, &
   SNESSetConvergenceTest, &
   SNESSetFromOptions, &
   SNESCreate, &
   MPI_Abort

contains

!--------------------------------------------------------------------------------------------------
!> @brief allocates all neccessary fields and fills them with data, potentially from restart info
!> @todo use sourced allocation, e.g. allocate(Fdot,source = F_lastInc)
!--------------------------------------------------------------------------------------------------
subroutine Polarisation_init(temperature)
 use, intrinsic :: iso_fortran_env                                                                  ! to get compiler_version and compiler_options (at least for gfortran >4.6 at the moment)
 use IO, only: &
   IO_intOut, &
   IO_read_JobBinaryFile, &
   IO_write_JobBinaryFile, &
   IO_timeStamp
 use debug, only : &
  debug_level, &
  debug_spectral, &
  debug_spectralRestart
 use FEsolving, only: &
   restartInc
 use DAMASK_interface, only: &
   getSolverJobName
 use DAMASK_spectral_Utilities, only: &
   Utilities_init, &
   Utilities_constitutiveResponse, &
   Utilities_updateGamma, &
   grid, &
   grid1Red, &
   geomSize, &
   wgt
 use mesh, only: &
   mesh_ipCoordinates, &
   mesh_deformedCoordsFFT
 use math, only: &
   math_invSym3333
   
 implicit none
 real(pReal), intent(inout) :: &
   temperature
#include <finclude/petscdmda.h90>
#include <finclude/petscsnes.h90>
 real(pReal), dimension(:,:,:,:,:), allocatable :: P
 real(pReal), dimension(3,3) :: &
   temp33_Real = 0.0_pReal
 real(pReal), dimension(3,3,3,3) :: &
   temp3333_Real = 0.0_pReal, &
   temp3333_Real2 = 0.0_pReal

 PetscErrorCode :: ierr
 PetscObject :: dummy
 PetscScalar, pointer, dimension(:,:,:,:) :: xx_psc, F, F_tau
 
 call Utilities_init()
 write(6,'(/,a)') ' <<<+-  DAMASK_spectral_solverPolarisation init  -+>>>'
 write(6,'(a)') ' $Id$'
 write(6,'(a16,a)')   ' Current time : ',IO_timeStamp()
#include "compilation_info.f90"

 allocate (P            (3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
!--------------------------------------------------------------------------------------------------
! allocate global fields
 allocate (F_lastInc    (3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
 allocate (F_lastInc2   (3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
 allocate (Fdot         (3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
 allocate (F_tau_lastInc(3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
 allocate (F_tauDot     (3,3,grid(1),grid(2),grid(3)),source = 0.0_pReal)
 allocate (inertiaField_fourier (grid1Red,grid(2),grid(3),3,3),source = cmplx(0.0_pReal,0.0_pReal,pReal))
    
!--------------------------------------------------------------------------------------------------
! PETSc Init
 call SNESCreate(PETSC_COMM_WORLD,snes,ierr); CHKERRQ(ierr)
 call DMDACreate3d(PETSC_COMM_WORLD,                               &
           DMDA_BOUNDARY_NONE, DMDA_BOUNDARY_NONE, DMDA_BOUNDARY_NONE, &
           DMDA_STENCIL_BOX,grid(1),grid(2),grid(3),PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE, &
           18,1,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,da,ierr)
 CHKERRQ(ierr)
 call DMCreateGlobalVector(da,solution_vec,ierr); CHKERRQ(ierr)
 call DMDASetLocalFunction(da,Polarisation_formResidual,ierr); CHKERRQ(ierr)
 call SNESSetDM(snes,da,ierr); CHKERRQ(ierr)
 call SNESSetConvergenceTest(snes,Polarisation_converged,dummy,PETSC_NULL_FUNCTION,ierr)
 CHKERRQ(ierr)
 call SNESSetFromOptions(snes,ierr); CHKERRQ(ierr)

!--------------------------------------------------------------------------------------------------
! init fields                 
 call DMDAVecGetArrayF90(da,solution_vec,xx_psc,ierr); CHKERRQ(ierr)                                ! places pointer xx_psc on PETSc data
 F => xx_psc(0:8,:,:,:)
 F_tau => xx_psc(9:17,:,:,:)
 if (restartInc == 1_pInt) then                                                                     ! no deformation (no restart)
   F_lastInc     = spread(spread(spread(math_I3,3,grid(1)),4,grid(2)),5,grid(3))                    ! initialize to identity
   F_lastInc2 = F_lastInc
   F_tau_lastInc = 2.0_pReal*F_lastInc
   F = reshape(F_lastInc,[9,grid(1),grid(2),grid(3)])
   F_tau = 2.0_pReal* F
 elseif (restartInc > 1_pInt) then 
   if (iand(debug_level(debug_spectral),debug_spectralRestart)/= 0) &
     write(6,'(/,a,'//IO_intOut(restartInc-1_pInt)//',a)') &
     'reading values of increment', restartInc - 1_pInt, 'from file'
   flush(6)
   call IO_read_jobBinaryFile(777,'F',&
                                                trim(getSolverJobName()),size(F))
   read (777,rec=1) F
   close (777)
   call IO_read_jobBinaryFile(777,'F_lastInc',&
                                                trim(getSolverJobName()),size(F_lastInc))
   read (777,rec=1) F_lastInc
   close (777)
   call IO_read_jobBinaryFile(777,'F_lastInc2',&
                                                trim(getSolverJobName()),size(F_lastInc2))
   read (777,rec=1) F_lastInc2
   close (777)
   F_aim         = reshape(sum(sum(sum(F,dim=4),dim=3),dim=2) * wgt, [3,3])                         ! average of F
   F_aim_lastInc = sum(sum(sum(F_lastInc,dim=5),dim=4),dim=3) * wgt                                 ! average of F_lastInc 
   call IO_read_jobBinaryFile(777,'F_tau',&
                                           trim(getSolverJobName()),size(F_tau))
   read (777,rec=1) F_tau
   close (777)
   call IO_read_jobBinaryFile(777,'F_tau_lastInc',&
                                        trim(getSolverJobName()),size(F_tau_lastInc))
   read (777,rec=1) F_tau_lastInc
   close (777)
   call IO_read_jobBinaryFile(777,'F_aimDot',trim(getSolverJobName()),size(f_aimDot))
   read (777,rec=1) f_aimDot
   close (777)
   call IO_read_jobBinaryFile(777,'C_volAvg',trim(getSolverJobName()),size(C_volAvg))
   read (777,rec=1) C_volAvg
   close (777)
   call IO_read_jobBinaryFile(777,'C_volAvgLastInc',trim(getSolverJobName()),size(C_volAvgLastInc))
   read (777,rec=1) C_volAvgLastInc
   close (777)
   call IO_read_jobBinaryFile(777,'C_ref',trim(getSolverJobName()),size(temp3333_Real))
   read (777,rec=1) C_minMaxAvg
   close (777)
 endif
 mesh_ipCoordinates = reshape(mesh_deformedCoordsFFT(geomSize,reshape(&
                                              F,[3,3,grid(1),grid(2),grid(3)])),[3,1,product(grid)])
 call Utilities_constitutiveResponse(F,F,temperature,0.0_pReal,P,temp3333_Real,temp3333_Real2,&
                                temp33_Real,.false.,math_I3)
 call DMDAVecRestoreArrayF90(da,solution_vec,xx_psc,ierr); CHKERRQ(ierr)

!--------------------------------------------------------------------------------------------------
! reference stiffness
 if (restartInc == 1_pInt) then                                                                     ! use initial stiffness as reference stiffness
   C_minMaxAvg = temp3333_Real2
   C_volAvg = temp3333_Real
 endif 

 call Utilities_updateGamma(temp3333_Real2,.True.)
 C_scale = temp3333_Real2
 S_scale = math_invSym3333(temp3333_Real2)
 
end subroutine Polarisation_init


!--------------------------------------------------------------------------------------------------
!> @brief solution for the Polarisation scheme with internal iterations
!--------------------------------------------------------------------------------------------------
type(tSolutionState) function &
  Polarisation_solution(incInfoIn,guess,timeinc,timeinc_old,loadCaseTime,P_BC,F_BC,temperature_bc,rotation_BC,density)
 use numerics, only: &
   update_gamma
 use math, only: &
   math_mul33x33 ,&
   math_mul3333xx33, &
   math_rotate_backward33, &
   math_invSym3333, &
   math_transpose33
use mesh, only: &
   mesh_ipCoordinates, &
   mesh_deformedCoordsFFT
 use IO, only: &
   IO_write_JobBinaryFile
 use DAMASK_spectral_Utilities, only: &
   grid, &
   geomSize, &
   tBoundaryCondition, &
   Utilities_forwardField, &
   Utilities_calculateRate, &
   Utilities_maskedCompliance, &
   Utilities_updateGamma, &
   cutBack
 use FEsolving, only: &
   restartWrite, &
   terminallyIll
 
 implicit none
#include <finclude/petscdmda.h90>
#include <finclude/petscsnes.h90>

!--------------------------------------------------------------------------------------------------
! input data for solution
 real(pReal), intent(in) :: &
   timeinc, &                                                                                       !< increment in time for current solution
   timeinc_old, &                                                                                   !< increment in time of last increment
   loadCaseTime, &                                                                                  !< remaining time of current load case
   temperature_bc, &
   density
 logical, intent(in) :: &
   guess
 type(tBoundaryCondition),      intent(in) :: &
   P_BC, &
   F_BC
 character(len=*), intent(in) :: &
   incInfoIn
 real(pReal), dimension(3,3), intent(in) :: rotation_BC
 
!--------------------------------------------------------------------------------------------------
! PETSc Data
 PetscScalar, dimension(:,:,:,:), pointer :: xx_psc, F, F_tau
 PetscErrorCode :: ierr   
 SNESConvergedReason :: reason

 integer(pInt) :: i, j, k
 real(pReal), dimension(3,3) :: F_lambda33

 incInfo = incInfoIn
 call DMDAVecGetArrayF90(da,solution_vec,xx_psc,ierr)
 F => xx_psc(0:8,:,:,:)
 F_tau => xx_psc(9:17,:,:,:)
 
!--------------------------------------------------------------------------------------------------
! restart information for spectral solver
 if (restartWrite) then
   write(6,'(/,a)') ' writing converged results for restart'
   flush(6)
   call IO_write_jobBinaryFile(777,'F',size(F))                                                     ! writing deformation gradient field to file
   write (777,rec=1) F
   close (777)
   call IO_write_jobBinaryFile(777,'F_lastInc',size(F_lastInc))                                     ! writing F_lastInc field to file
   write (777,rec=1) F_lastInc
   close (777)
   call IO_write_jobBinaryFile(777,'F_tau',size(F_tau))                                             ! writing deformation gradient field to file
   write (777,rec=1) F_tau
   close (777)
   call IO_write_jobBinaryFile(777,'F_tau_lastInc',size(F_tau_lastInc))                             ! writing F_lastInc field to file
   write (777,rec=1) F_tau_lastInc
   close (777)
   call IO_write_jobBinaryFile(777,'F_aimDot',size(F_aimDot))
   write (777,rec=1) F_aimDot
   close(777)
   call IO_write_jobBinaryFile(777,'C_volAvg',size(C_volAvg))
   write (777,rec=1) C_volAvg
   close(777)
   call IO_write_jobBinaryFile(777,'C_volAvgLastInc',size(C_volAvgLastInc))
   write (777,rec=1) C_volAvgLastInc
   close(777)
 endif 
 Polarisation_solution%converged =.false.

 if (cutBack) then 
   F_aim = F_aim_lastInc
   F_tau= reshape(F_tau_lastInc,[9,grid(1),grid(2),grid(3)]) 
   F    = reshape(F_lastInc,    [9,grid(1),grid(2),grid(3)]) 
   C_volAvg = C_volAvgLastInc
 else
   C_volAvgLastInc = C_volAvg
!--------------------------------------------------------------------------------------------------
! calculate rate for aim
   if (F_BC%myType=='l') then                                                                       ! calculate f_aimDot from given L and current F
     f_aimDot = F_BC%maskFloat * math_mul33x33(F_BC%values, F_aim)
   elseif(F_BC%myType=='fdot') then                                                                 ! f_aimDot is prescribed
     f_aimDot = F_BC%maskFloat * F_BC%values
   elseif(F_BC%myType=='f') then                                                                    ! aim at end of load case is prescribed
     f_aimDot = F_BC%maskFloat * (F_BC%values -F_aim)/loadCaseTime
   endif
   if (guess) f_aimDot  = f_aimDot + P_BC%maskFloat * (F_aim - F_aim_lastInc)/timeinc_old
   F_aim_lastInc = F_aim

!--------------------------------------------------------------------------------------------------
! update coordinates and rate and forward last inc
   mesh_ipCoordinates = reshape(mesh_deformedCoordsFFT(geomSize,reshape(&
                                            F,[3,3,grid(1),grid(2),grid(3)])),[3,1,product(grid)])
   Fdot =  Utilities_calculateRate(math_rotate_backward33(f_aimDot,rotation_BC), &
                  timeinc_old,guess,F_lastInc,reshape(F,[3,3,grid(1),grid(2),grid(3)]))
   F_tauDot =  Utilities_calculateRate(math_rotate_backward33(2.0_pReal*f_aimDot,rotation_BC), &
                  timeinc_old,guess,F_tau_lastInc,reshape(F_tau,[3,3,grid(1),grid(2),grid(3)]))  
   F_lastInc2 = F_lastInc
   F_lastInc     = reshape(F,       [3,3,grid(1),grid(2),grid(3)])
   F_tau_lastInc = reshape(F_tau,[3,3,grid(1),grid(2),grid(3)])
 endif
 F_aim = F_aim + f_aimDot * timeinc

!--------------------------------------------------------------------------------------------------
! update local deformation gradient
 F     = reshape(Utilities_forwardField(timeinc,F_lastInc,Fdot, &                                      ! ensure that it matches rotated F_aim
                               math_rotate_backward33(F_aim,rotation_BC)),[9,grid(1),grid(2),grid(3)])
 F_tau = reshape(Utilities_forwardField(timeinc,F_tau_lastInc,F_taudot),  [9,grid(1),grid(2),grid(3)]) ! does not have any average value as boundary condition
 if (.not. guess) then                                                                                 ! large strain forwarding
   do k = 1_pInt, grid(3); do j = 1_pInt, grid(2); do i = 1_pInt, grid(1)
      F_lambda33 = reshape(F_tau(:,i,j,k)-F(:,i,j,k),[3,3])
      F_lambda33 = math_mul3333xx33(S_scale,math_mul33x33(F_lambda33, &
                                  math_mul3333xx33(C_scale,&
                                                   math_mul33x33(math_transpose33(F_lambda33),&
                                                                 F_lambda33) -math_I3))*0.5_pReal)&
                              + math_I3
      F_tau(:,i,j,k) = reshape(F_lambda33,[9])+F(:,i,j,k)
   enddo; enddo; enddo
 endif
 call DMDAVecRestoreArrayF90(da,solution_vec,xx_psc,ierr)
 CHKERRQ(ierr)

!--------------------------------------------------------------------------------------------------
! update stiffness (and gamma operator)
 S = Utilities_maskedCompliance(rotation_BC,P_BC%maskLogical,C_volAvg)
 if (update_gamma) then
   call Utilities_updateGamma(C_minMaxAvg,restartWrite)
   C_scale = C_minMaxAvg
   S_scale = math_invSym3333(C_minMaxAvg)
 endif  
 
 ForwardData = .True.
 mask_stress = P_BC%maskFloat
 params%P_BC = P_BC%values
 params%rotation_BC = rotation_BC
 params%timeinc = timeinc
 params%timeincOld = timeinc_old
 params%temperature = temperature_bc
 params%density = density

!--------------------------------------------------------------------------------------------------
! solve BVP 
 call SNESSolve(snes,PETSC_NULL_OBJECT,solution_vec,ierr)
 CHKERRQ(ierr)

!--------------------------------------------------------------------------------------------------
! check convergence
 call SNESGetConvergedReason(snes,reason,ierr)
 CHKERRQ(ierr)
 Polarisation_solution%termIll = terminallyIll
 terminallyIll = .false.
 Polarisation_solution%converged = .true.
 if (reason < 1 ) Polarisation_solution%converged = .false.
 Polarisation_solution%iterationsNeeded = totalIter

end function Polarisation_solution


!--------------------------------------------------------------------------------------------------
!> @brief forms the Polarisation residual vector
!--------------------------------------------------------------------------------------------------
subroutine Polarisation_formResidual(in,x_scal,f_scal,dummy,ierr)
 use numerics, only: &
   itmax, &
   itmin, &
   polarAlpha, &
   polarBeta
 use IO, only: &
   IO_intOut
 use math, only: &
   math_rotate_backward33, &
   math_transpose33, &
   math_mul3333xx33, &
   math_invSym3333, &
   math_mul33x33, &
   PI
 use DAMASK_spectral_Utilities, only: &
   grid, &
   geomSize, &
   wgt, &
   field_real, &
   field_fourier, &
   Utilities_FFTforward, &
   Utilities_fourierConvolution, &
   Utilities_inverseLaplace, &
   Utilities_FFTbackward, &
   Utilities_constitutiveResponse, &
   Utilities_divergenceRMS, &
   Utilities_curlRMS
 use debug, only: &
   debug_level, &
   debug_spectral, &
   debug_spectralRotation
 use homogenization, only: &
   materialpoint_dPdF

 implicit none
!--------------------------------------------------------------------------------------------------
! strange syntax in the next line because otherwise macros expand beyond 132 character limit 
 DMDALocalInfo,        dimension(&
   DMDA_LOCAL_INFO_SIZE) :: &
   in
 PetscScalar, target, dimension(3,3,2, &
   XG_RANGE,YG_RANGE,ZG_RANGE) :: &
   x_scal
 PetscScalar, target, dimension(3,3,2, &
   X_RANGE,Y_RANGE,Z_RANGE) :: &
   f_scal
 PetscScalar, pointer, dimension(:,:,:,:,:) :: &
   F, &
   F_tau, &
   residual_F, &
   residual_F_tau
 PetscInt :: &
   PETScIter, &
   nfuncs
 PetscObject :: dummy
 PetscErrorCode :: ierr
 integer(pInt) :: &
   i, j, k, e
 
 F              => x_scal(1:3,1:3,1,&
  XG_RANGE,YG_RANGE,ZG_RANGE)
 F_tau          => x_scal(1:3,1:3,2,&
  XG_RANGE,YG_RANGE,ZG_RANGE)
 residual_F     => f_scal(1:3,1:3,1,&
  X_RANGE,Y_RANGE,Z_RANGE)
 residual_F_tau => f_scal(1:3,1:3,2,&
  X_RANGE,Y_RANGE,Z_RANGE)
 
 call SNESGetNumberFunctionEvals(snes,nfuncs,ierr); CHKERRQ(ierr)
 call SNESGetIterationNumber(snes,PETScIter,ierr); CHKERRQ(ierr)

 if(nfuncs== 0 .and. PETScIter == 0) totalIter = -1_pInt                                            ! new increment
 if (totalIter <= PETScIter) then                                                                   ! new iteration
!--------------------------------------------------------------------------------------------------
! report begin of new iteration
   totalIter = totalIter + 1_pInt
   write(6,'(1x,a,3(a,'//IO_intOut(itmax)//'))') trim(incInfo), &
                    ' @ Iteration ', itmin, '≤',totalIter, '≤', itmax
   if (iand(debug_level(debug_spectral),debug_spectralRotation) /= 0) &
   write(6,'(/,a,/,3(3(f12.7,1x)/))',advance='no') ' deformation gradient aim (lab) =', &
                                 math_transpose33(math_rotate_backward33(F_aim,params%rotation_BC))
   write(6,'(/,a,/,3(3(f12.7,1x)/))',advance='no') ' deformation gradient aim =', &
                                 math_transpose33(F_aim)
   flush(6)
 endif

!--------------------------------------------------------------------------------------------------
! evaluate inertia
 dynamic: if (params%density > 0.0_pReal) then
   residual_F = ((F - F_lastInc)/params%timeinc - (F_lastInc - F_lastInc2)/params%timeincOld)/&
                                                  ((params%timeinc + params%timeincOld)/2.0_pReal)
   residual_F = params%density*product(geomSize/grid)*residual_F
   field_real = 0.0_pReal
   field_real(1:grid(1),1:grid(2),1:grid(3),1:3,1:3) = reshape(residual_F,[grid(1),grid(2),grid(3),3,3],&
                                                               order=[4,5,1,2,3])                   ! field real has a different order
   call Utilities_FFTforward()
   call Utilities_inverseLaplace()
   inertiaField_fourier = field_fourier
 else dynamic
   inertiaField_fourier = cmplx(0.0_pReal,0.0_pReal,pReal)
 endif dynamic
  
!--------------------------------------------------------------------------------------------------
! 
 field_real = 0.0_pReal
 do k = 1_pInt, grid(3); do j = 1_pInt, grid(2); do i = 1_pInt, grid(1)
   field_real(i,j,k,1:3,1:3) = &
     polarBeta*math_mul3333xx33(C_scale,F(1:3,1:3,i,j,k) - math_I3) -&
     polarAlpha*math_mul33x33(F(1:3,1:3,i,j,k), &
                              math_mul3333xx33(C_scale,F_tau(1:3,1:3,i,j,k) - F(1:3,1:3,i,j,k) - math_I3))

 enddo; enddo; enddo
 
!--------------------------------------------------------------------------------------------------
! doing convolution in Fourier space 
 call Utilities_FFTforward()
 field_fourier = field_fourier + polarAlpha*inertiaField_fourier
 call Utilities_fourierConvolution(math_rotate_backward33(polarBeta*F_aim,params%rotation_BC)) 
 call Utilities_FFTbackward()

!--------------------------------------------------------------------------------------------------
! constructing residual                         
 residual_F_tau = polarBeta*F - reshape(field_real(1:grid(1),1:grid(2),1:grid(3),1:3,1:3),&
                                      [3,3,grid(1),grid(2),grid(3)],order=[3,4,5,1,2])

!--------------------------------------------------------------------------------------------------
! evaluate constitutive response
 P_avLastEval = P_av
 call Utilities_constitutiveResponse(F_lastInc,F - residual_F_tau/polarBeta,params%temperature,params%timeinc, &
                                     residual_F,C_volAvg,C_minMaxAvg,P_av,ForwardData,params%rotation_BC)
 ForwardData = .False.

!--------------------------------------------------------------------------------------------------
! calculate divergence
 field_real = 0.0_pReal
 field_real = reshape(residual_F,[grid(1),grid(2),grid(3),3,3],order=[4,5,1,2,3]) 
 call Utilities_FFTforward()
 err_div = Utilities_divergenceRMS()
 call Utilities_FFTbackward()
 
!--------------------------------------------------------------------------------------------------
! constructing residual
 e = 0_pInt
 do k = 1_pInt, grid(3); do j = 1_pInt, grid(2); do i = 1_pInt, grid(1)
   e = e + 1_pInt
   residual_F(1:3,1:3,i,j,k) = &
     math_mul3333xx33(math_invSym3333(materialpoint_dPdF(:,:,:,:,1,e) + C_scale), &
                      residual_F(1:3,1:3,i,j,k) - math_mul33x33(F(1:3,1:3,i,j,k), &
                      math_mul3333xx33(C_scale,F_tau(1:3,1:3,i,j,k) - F(1:3,1:3,i,j,k) - math_I3))) &
   + residual_F_tau(1:3,1:3,i,j,k)
 enddo; enddo; enddo
 
!--------------------------------------------------------------------------------------------------
! calculating curl
 field_real = 0.0_pReal
 field_real = reshape(F,[grid(1),grid(2),grid(3),3,3],order=[4,5,1,2,3]) 
 call Utilities_FFTforward()
 err_curl = Utilities_curlRMS()
 call Utilities_FFTbackward()
 
end subroutine Polarisation_formResidual


!--------------------------------------------------------------------------------------------------
!> @brief convergence check
!--------------------------------------------------------------------------------------------------
subroutine Polarisation_converged(snes_local,PETScIter,xnorm,snorm,fnorm,reason,dummy,ierr)
 use numerics, only: &
   itmax, &
   itmin, &
   err_div_tolRel, &
   err_div_tolAbs, &
   err_curl_tolRel, &
   err_curl_tolAbs, &
   err_stress_tolabs, &
   err_stress_tolrel
 use math, only: &
   math_mul3333xx33
 use FEsolving, only: &
   terminallyIll

 implicit none
 SNES :: snes_local
 PetscInt :: PETScIter
 PetscReal :: &
   xnorm, &
   snorm, &
   fnorm
 SNESConvergedReason :: reason
 PetscObject :: dummy
 PetscErrorCode ::ierr
 real(pReal) :: &
   curlTol, &
   divTol, &
   stressTol
     
!--------------------------------------------------------------------------------------------------
! stress BC handling
 F_aim = F_aim - math_mul3333xx33(S, ((P_av - params%P_BC)))                                        ! S = 0.0 for no bc
 err_stress = maxval(abs(mask_stress * (P_av - params%P_BC)))                                       ! mask = 0.0 for no bc

!--------------------------------------------------------------------------------------------------
! error calculation
 curlTol    = max(maxval(abs(F_aim-math_I3))*err_curl_tolRel,err_curl_tolAbs)
 divTol     = max(maxval(abs(P_av))         *err_div_tolRel,err_div_tolAbs)
 stressTol  = max(maxval(abs(P_av))    *err_stress_tolrel,err_stress_tolabs)

 converged: if ((totalIter >= itmin .and. &
                           all([ err_div/divTol, &
                                 err_curl/curlTol, &
                                 err_stress/stressTol       ] < 1.0_pReal)) &
             .or.    terminallyIll) then
   reason = 1
 elseif (totalIter >= itmax) then converged
   reason = -1
 else converged
   reason = 0
 endif converged

!--------------------------------------------------------------------------------------------------
! report
 write(6,'(1/,a)') ' ... reporting .............................................................'
 write(6,'(/,a,f12.2,a,es8.2,a,es9.2,a)') ' error curl =       ', &
            err_curl/curlTol,' (',err_curl,' -,   tol =',curlTol,')'
 write(6,'(a,f12.2,a,es8.2,a,es9.2,a)') ' error divergence = ', &
            err_div/divTol,  ' (',err_div,' / m, tol =',divTol,')'
 write(6,'(a,f12.2,a,es8.2,a,es9.2,a)')   ' error stress BC =  ', &
            err_stress/stressTol, ' (',err_stress, ' Pa,  tol =',stressTol,')' 
 write(6,'(/,a)') ' ==========================================================================='
 flush(6) 

end subroutine Polarisation_converged

!--------------------------------------------------------------------------------------------------
!> @brief destroy routine
!--------------------------------------------------------------------------------------------------
subroutine Polarisation_destroy()
 use DAMASK_spectral_Utilities, only: &
   Utilities_destroy
 
 implicit none
 PetscErrorCode :: ierr

 call VecDestroy(solution_vec,ierr); CHKERRQ(ierr)
 call SNESDestroy(snes,ierr); CHKERRQ(ierr)
 call DMDestroy(da,ierr); CHKERRQ(ierr)
 call PetscFinalize(ierr); CHKERRQ(ierr)
 call Utilities_destroy()

end subroutine Polarisation_destroy

end module DAMASK_spectral_SolverPolarisation