TDMA.f90 - Solution of system of linear equations by Thomas method

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!Sample program for solving Lid-driven cavity flow test using SIMPLE-algorithm
! solution of linear system of equations by Thomas algorithm modul
!Copyright (C) 2010  Michail Kiričkov
!Copyright (C) 2016  Michail Kiričkov, Kaunas University for Technology

!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; either version 2
!of the License, or (at your option) any later version.

!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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

!**********************************************************************
Subroutine TDMA_1(NF)
include 'icomm_1.f90'  
DOUBLE PRECISION  P(nx),Q(nx)
!-----------------------------------------------------------
	Do 101 J =  2, NYmax
	 	    P(1) =  0.		    
			Q(1) =  F(1,j,nf)   
			P(NXmaxC) = 0.
			Q(NXmaxC) = F(NXmaxC,j,nf) 
 !		Forward Elimination
      Do 10 i = 2,NXmaxC-1
			temp =  Ap(i,j,nf) - Aw(i,j) * P(i-1)
			Spp= Sp(i,j,nf) + As(i,j) * F(i,j-1,nf) + &
						      An(i,j) * F(i,j+1,nf)  
			P(i) = Ae(i,j) / temp
			Q(i) = (Spp + Aw(i,j)*Q(i-1)) / temp
	10    continue
!		 Back Substitution
	  Do 20 i = NXmaxC-1,1,-1
          F(i,j,nf) = P(i)*F(i+1,j,nf) + Q(i)
		20    continue
     101 continue 
!-----------------------------------------------------------
	Do 301 J =  NYmax,2,-1
	 	    P(1) =  0.		    
    		Q(1) =  F(1,j,nf)   
			P(NXmaxC) = 0.
			Q(NXmaxC) = F(NXmaxC,j,nf) 
 !		Forward Elimination
	      Do 32 i = 2,NXmaxC-1
			temp =  Ap(i,j,nf) - Aw(i,j) * P(i-1)
			Spp= Sp(i,j,nf) + As(i,j) * F(i,j-1,nf) + &
						      An(i,j) * F(i,j+1,nf)  
			P(i) = Ae(i,j) / temp
			Q(i) = (Spp + Aw(i,j)*Q(i-1)) / temp
		32    continue
!		 Back Substitution
	  Do 30 i = NXmaxC-1,2,-1
         F(i,j,nf) = P(i)*F(i+1,j,nf) + Q(i)
		30    continue
     301 continue 
!--------------------------------------------------------------
Return
End