!     
!     CalculiX - A 3-dimensional finite element program
!     Copyright (C) 1998-2025 Guido Dhondt
!     
!     This program 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(version 2);
!     
!     
!     This program 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 this program; if not, write to the Free Software
!     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
!     
      subroutine feasibledirections(inpc,textpart,istat,n,key,iline,
     &     ipol,inl,ipoinp,inp,ipoinpc,nmethod,istep,ier,tmax,tinc)          
!     
!     reading the input deck: *FEASIBLE DIRECTION
!     
      implicit none
!     
      character*1 inpc(*)
      character*132 textpart(16)
!     
      integer nmethod,nobject,i,n,key,istat,istep,iline,ipol,inl,
     &     ipoinp(2,*),inp(3,*),ipoinpc(0:*),ier
!     
      real*8 tmax,tinc
!     
      tmax=0.d0
      tinc=-1.d0
!     
      if(istep.lt.1) then
        write(*,*) '*ERROR reading *FEASIBLE DIRECTION:'
        write(*,*) '       *FEASIBLE DIRECTION can only be used'
        write(*,*) '       within a STEP'    
        ier=1
        return
      endif
!     
      nmethod=16 
!     
!     read optimization method
!     tmax=1.5: Gradient Descent Akin Method (GDAM, default)
!     tmax=2.5: Gradient Projection Method (GPM)
!     
      do i=2,n
        if(textpart(i)(1:7).eq.'METHOD=') then
          if(textpart(i)(8:22).eq.'GRADIENTDESCENT') then
            tmax=1.5
          elseif(textpart(i)(8:25).eq.'GRADIENTPROJECTION') then
            tmax=2.5
          else
            write(*,*) 
            write(*,*) '*WARNING reading *FEASIBLE DIRECTION; '     
            write(*,*) '         Method for computation of '     
            write(*,*) '         *FEASIBLE DIRECTION not valid;'
            write(*,*) '         Gradient Descent taken as default' 
            write(*,*) ' '
            call inputwarning(inpc,ipoinpc,iline,
     &           "*FEASIBLEDIRECTION%")
          endif
        endif
      enddo
!     
      if(tmax.lt.1.d0) then
        tmax=1.5
        write(*,*)
        write(*,*) '*WARNING reading *FEASIBLE DIRECTION; '     
        write(*,*) '         Method for computation of '     
        write(*,*) '         *FEASIBLE DIRECTION not specified;'
        write(*,*) '         Gradient Descent taken as default'
        write(*,*) ' '
        call inputwarning(inpc,ipoinpc,iline,"*FEASIBLEDIRECTION%")
      endif          
!     
      call getnewline(inpc,textpart,istat,n,key,iline,ipol,inl,
     &     ipoinp,inp,ipoinpc)
      if((istat.lt.0).or.(key.eq.1)) then
        write(*,*) '*ERROR reading *FEASIBLE DIRECTION'
        write(*,*) '       no size of mesh modification specified'
        ier=1
        return
      endif
!     
      read(textpart(1)(1:20),'(f20.0)',iostat=istat) tinc
      if(istat.gt.0) then
        call inputerror(inpc,ipoinpc,iline,
     &       "*FEASIBLE DIRECTION%",ier)
        return
      endif
!     
!     tinc is the maximum size of the requested mesh modification     
!     for optimization 
!     
      if(tinc.le.0.d0) then
        write(*,*) '*ERROR reading *FEASIBLE DIRECTION'
        write(*,*) '       no size of mesh modification specified'
        ier=1
        return
      endif
!     
      call getnewline(inpc,textpart,istat,n,key,iline,ipol,inl,
     &     ipoinp,inp,ipoinpc)     
!     
      return
      end      
      
