more flexibility for the L in the load case

Note that mixed boundary conditions for L introduce an ambiguity.
Consider:

L = [[1.0, x, x],
     [  0, 0, 0],
     [  0, 0, 0]]
P = [[x, 0, 0],
     [x, x, x],
     [x, x, x]]

What we need is F^(n+1)=F_dot^(n+1) x Delta_t, where F_dot^(n+1) is
F_dot^(n+1)_ij = L_ik F^n_kj.

So component F_11 has contributions from L_12 and L_13. We first assume
L_12=L_13=0 and then choose F^(n+1)_12 and F^(n+1)_13 to get
P_12=P_13=0. This implicitly gives a solution for L_12 and L_13, which
is however only one out of infinitely many.

src/IO.f90

@@ -504,8 +504,6 @@ subroutine IO_error(error_ID,el,ip,g,instance,ext_msg)
 ! errors related to the grid solver
     case (831)
       msg = 'mask consistency violated in grid load case'
-    case (832)
-      msg = 'ill-defined L (line partly defined) in grid load case'
     case (833)
       msg = 'non-positive ratio for geometric progression'
     case (834)

src/grid/DAMASK_grid.f90

@@ -218,12 +218,6 @@ program DAMASK_grid
     reportAndCheck: if (worldrank == 0) then
       print'(/,a,i0)', ' load case: ', l
       print*, ' estimate_rate:', loadCases(l)%estimate_rate
-      if (loadCases(l)%deformation%myType == 'L') then
-        do j = 1, 3
-          if (any(loadCases(l)%deformation%mask(j,1:3) .eqv. .true.) .and. &
-              any(loadCases(l)%deformation%mask(j,1:3) .eqv. .false.)) errorID = 832                ! each row should be either fully or not at all defined
-        enddo
-      endif
       if (loadCases(l)%deformation%myType == 'F') then
         print*, ' F:'
       else

src/grid/grid_mech_FEM.f90

@@ -370,7 +370,7 @@ subroutine grid_mechanical_FEM_forward(cutBack,guess,Delta_t,Delta_t_old,t_remai
     ! calculate rate for aim
     if     (deformation_BC%myType=='L') then                                                        ! calculate F_aimDot from given L and current F
       F_aimDot = F_aimDot &
-               + merge(.0_pReal,matmul(deformation_BC%values, F_aim_lastInc),deformation_BC%mask)
+               + matmul(merge(.0_pReal,deformation_BC%values,deformation_BC%mask),F_aim_lastInc)
     elseif (deformation_BC%myType=='dot_F') then                                                    ! F_aimDot is prescribed
       F_aimDot = F_aimDot &
                + merge(.0_pReal,deformation_BC%values,deformation_BC%mask)

src/grid/grid_mech_spectral_basic.f90

@@ -321,7 +321,7 @@ subroutine grid_mechanical_spectral_basic_forward(cutBack,guess,Delta_t,Delta_t_
     ! calculate rate for aim
     if     (deformation_BC%myType=='L') then                                                        ! calculate F_aimDot from given L and current F
       F_aimDot = F_aimDot &
-               + merge(.0_pReal,matmul(deformation_BC%values, F_aim_lastInc),deformation_BC%mask)
+               + matmul(merge(.0_pReal,deformation_BC%values,deformation_BC%mask),F_aim_lastInc)
     elseif (deformation_BC%myType=='dot_F') then                                                    ! F_aimDot is prescribed
       F_aimDot = F_aimDot &
                + merge(.0_pReal,deformation_BC%values,deformation_BC%mask)

src/grid/grid_mech_spectral_polarisation.f90

@@ -357,7 +357,7 @@ subroutine grid_mechanical_spectral_polarisation_forward(cutBack,guess,Delta_t,D
     ! calculate rate for aim
     if     (deformation_BC%myType=='L') then                                                        ! calculate F_aimDot from given L and current F
       F_aimDot = F_aimDot &
-               + merge(.0_pReal,matmul(deformation_BC%values, F_aim_lastInc),deformation_BC%mask)
+               + matmul(merge(.0_pReal,deformation_BC%values,deformation_BC%mask),F_aim_lastInc)
     elseif (deformation_BC%myType=='dot_F') then                                                    ! F_aimDot is prescribed
       F_aimDot = F_aimDot &
                + merge(.0_pReal,deformation_BC%values,deformation_BC%mask)