PROGRAM d03ebfe

!      D03EBF Example Program Text

!      Mark 23 Release. NAG Copyright 2011.

!      .. Use Statements ..
       USE nag_library, ONLY : d03ebf, nag_wp
!      .. Implicit None Statement ..
       IMPLICIT NONE
!      .. Parameters ..
       REAL (KIND=nag_wp), PARAMETER   :: one = 1.0_nag_wp
       REAL (KIND=nag_wp), PARAMETER   :: two = 2.0_nag_wp
       REAL (KIND=nag_wp), PARAMETER   :: zero = 0.0_nag_wp
       INTEGER, PARAMETER              :: nin = 5, nout = 6
!      .. Local Scalars ..
       REAL (KIND=nag_wp)              :: aparam, conchn, conres
       INTEGER                         :: i, ifail, itcoun, itmax, itused,     &
                                          ixn, iyn, j, lda, n1, n2, ndir
!      .. Local Arrays ..
       REAL (KIND=nag_wp), ALLOCATABLE :: a(:,:), b(:,:), c(:,:), chngs(:),    &
                                          d(:,:), e(:,:), q(:,:), resids(:),   &
                                          t(:,:), wrksp1(:,:), wrksp2(:,:),    &
                                          wrksp3(:,:), x(:), y(:)
!      .. Intrinsic Functions ..
       INTRINSIC                          cos, exp
!      .. Executable Statements ..
       WRITE (nout,*) 'D03EBF Example Program Results'
       WRITE (nout,*)
!      Skip heading in data file
       READ (nin,*)
       READ (nin,*) n1, n2, itmax
       lda = n1
       ALLOCATE (a(lda,n2),b(lda,n2),c(lda,n2),chngs(itmax),d(lda,n2), &
          e(lda,n2),q(lda,n2),resids(itmax),t(lda,n2),wrksp1(lda,n2), &
          wrksp2(lda,n2),wrksp3(lda,n2),x(n1),y(n2))

       READ (nin,*) x(1:n1)
       READ (nin,*) y(1:n2)
       READ (nin,*) conres, conchn
       READ (nin,*) ndir
       aparam = one
       itcoun = 0
!      Set up difference equation coefficients, source terms and
!      initial conditions.
       a(1:n1,1:n2) = zero
       b(1:n1,1:n2) = zero
       c(1:n1,1:n2) = zero
       d(1:n1,1:n2) = zero
       e(1:n1,1:n2) = zero
       q(1:n1,1:n2) = zero
       t(1:n1,1:n2) = zero
!      Non-zero specification for internal nodes
       DO j = 2, n2 - 1
          DO i = 2, n1 - 1
             a(i,j) = two/((y(j)-y(j-1))*(y(j+1)-y(j-1)))
             e(i,j) = two/((y(j+1)-y(j))*(y(j+1)-y(j-1)))
             b(i,j) = two/((x(i)-x(i-1))*(x(i+1)-x(i-1)))
             d(i,j) = two/((x(i+1)-x(i))*(x(i+1)-x(i-1)))
             c(i,j) = -a(i,j) - b(i,j) - d(i,j) - e(i,j)
          END DO
       END DO
!      Non-zero specification for boundary nodes
       q(1:n1,1) = exp((x(1:n1)+one)/y(n2))*cos(y(1)/y(n2))
       q(1:n1,n2) = exp((x(1:n1)+one)/y(n2))*cos(y(n2)/y(n2))
       q(1,1:n2) = exp((x(1)+one)/y(n2))*cos(y(1:n2)/y(n2))
       q(n1,1:n2) = exp((x(n1)+one)/y(n2))*cos(y(1:n2)/y(n2))

!      ifail: behaviour on error exit   
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
       ifail = 0
       CALL d03ebf(n1,n2,lda,a,b,c,d,e,q,t,aparam,itmax,itcoun,itused,ndir, &
          ixn,iyn,conres,conchn,resids,chngs,wrksp1,wrksp2,wrksp3,ifail)

       WRITE (nout,*) 'Iteration      Maximum        Maximum'
       WRITE (nout,*) ' number        residual        change'
       WRITE (nout,99999) (i,resids(i),chngs(i),i=1,itused)
       WRITE (nout,*)
       WRITE (nout,*) 'Table of calculated function values'
       WRITE (nout,*)
       WRITE (nout,99998) (i,i=1,6)
       WRITE (nout,*) ' J'
       DO j = 1, n2
          WRITE (nout,99997) j, (t(i,j),i=1,n1)
       END DO

99999  FORMAT (2X,I2,10X,E11.4,4X,E11.4)
99998  FORMAT (1X,' I',1X,6(I4,7X))
99997  FORMAT (1X,I2,1X,6(F9.3,2X))
    END PROGRAM d03ebfe