*
* $Id: esolve.F,v 1.1.1.1 1996/04/01 15:02:18 mclareni Exp $
*
* $Log: esolve.F,v $
* Revision 1.1.1.1  1996/04/01 15:02:18  mclareni
* Mathlib gen
*
*
#include "gen/pilot.h"
      SUBROUTINE ESOLVE(M1,N,AD,BD,CD,DELTAY,IBCX,ALFAS,BETAS,ALFAN,
     +BETAN,POT,IKIND)
      COMMON/FW1/W1(774)/FW2/W2(100)
      DIMENSION POT(M1,N)
      DATA PI/3.141592653589793/
      M=M1-1
      COEFY=2.*DELTAY
      IF(BETAS.EQ.0.) GOTO 50
      IBCYS=2
      COEF1S=COEFY/BETAS
      COEF2S=ALFAS*COEF1S
      GOTO 53
 50   IBCYS=1
      DIV=1./ALFAS
      DO 51 I=1,M1
 51   W1(2*M1+I)=DIV*W1(2*M1+I)
 53   IF(BETAN.EQ.0.) GOTO 54
      IBCYN=2
      COEF1N=COEFY/BETAN
      COEF2N=ALFAN*COEF1N
      GOTO 56
 54   IBCYN=1
      DIV=1./ALFAN
      DO 55 I=1,M1
 55   W1(3*M1+I)=DIV*W1(3*M1+I)
 56   CONTINUE
      XM=M
      NA=N-1
      NAA=N-2
      JUMP=1
      PIOVM=PI/XM
      IF(IBCX.EQ.1) PIOVM=2.*PIOVM
      IF(IBCX.EQ.4) PIOVM=.5*PIOVM
      DUM1=.5*BD
      XNORTH=AD+DUM1
      XSOUTH=AD-DUM1
      CENT=2.*(1.+AD)-CD
      GOTO(100,200,300),IKIND
C
C   THIS PART OF THE SUBROUTINE IS USED
C   WHEN IKIND=1 THAT IS IN THE ELLIPTIC CASE
C   AND SOLVES THE THREE-POINT RECURRENCE
C   FORMULA THROUGH GAUSS ELIMINATION
C
 100  GOTO(110,120,130,135),IBCX
 110  IMIN=1
      IMAX=M/2+1
      GOTO 140
 120  IMIN=1
      IMAX=M1
      GOTO 140
 130  IMIN=2
      IMAX=M
      GOTO 140
 135  IMIN=2
      IMAX=M1
      JUMP=2
 140  AA=1.
      IOUT=0
      ISUB=0
 141  DO 1 I=IMIN,IMAX,JUMP
      XI=I-1-ISUB
      H=2.*COS(PIOVM*XI)
      FCENT=CENT-AA*H
      DEN=1./FCENT
      GOTO(111,112),IBCYS
 111  W2(2)=DEN*XNORTH
      W2(N+2)=DEN*(XSOUTH*W1(2*M1+I)-POT(I,2))
      JMIN=3
      JMAX=NAA
      GOTO 113
 112  DEN=1./(FCENT-XSOUTH*COEF2S)
      W2(1)=DEN*(XSOUTH+XNORTH)
      W2(N+1)=-DEN*(POT(I,1)+XSOUTH*COEF1S*W1(2*M1+I))
      JMIN=2
      JMAX=NA
 113  DO 2 J=JMIN,NA
      DEN=1./(FCENT-XSOUTH*W2(J-1))
      W2(J)=DEN*XNORTH
 2    W2(N+J)=DEN*(XSOUTH*W2(NA+J)-POT(I,J))
      GOTO(121,122),IBCYN
 121  POT(I,N)=W1(3*M1+I)
      GOTO 123
 122  IF(IBCX.EQ.4) GOTO 126
      IF(IBCYS.EQ.2.AND.IBCX.NE.3) GOTO 124
      GOTO 126
 124  IF(I.EQ.1) GOTO 125
 126  DEN=1./(FCENT-W2(NA)*(XSOUTH+XNORTH)+XNORTH*COEF2N)
      POT(I,N)=DEN*(-POT(I,N)+XNORTH*COEF1N*W1(3*M1+I)
     ++W2(N+NA)*(XSOUTH+XNORTH))
      GOTO 123
 125  POT(1,N)=0.
 123  POT(I,1)=W1(2*M1+I)
      DO 3 J=1,JMAX
      K=N-J
 3    POT(I,K)=W2(K)*POT(I,K+1)+W2(N+K)
 1    CONTINUE
      IOUT=IOUT+1
      IF(IOUT.EQ.2) RETURN
      IF(IBCX.NE.1) GOTO 143
      IMIN=IMAX+1
      IMAX=M
      AA=-1.
      GOTO 141
 143  IF(IBCX.NE.4) RETURN
      ISUB=ISUB+1
      IMIN=3
      AA=-1.
      GOTO 141
C
C
C   THIS PART OF THE SUBROUTINE IS USED
C   WHEN IKIND=2 THAT IS IN THE PARABOLIC CASE
C   AND SOLVES THE TWO-POINT RECURRENCE
C   FORMULA STEP BY STEP
C
C
 200  GOTO(210,220,230,235),IBCX
 210  IMIN=1
      IMAX=M/2+1
      GOTO 240
 220  IMIN=1
      IMAX=M1
      GOTO 240
 230  IMIN=2
      IMAX=M
      GOTO 240
 235  IMIN=2
      IMAX=M1
      JUMP=2
 240  AA=1.
      IOUT=0
      ISUB=0
      DUM2=2.*BD
      DUMUP=-2.+DUM2+CD
      DUMLO=-2.-DUM2+CD
 241  DO 11 I=IMIN,IMAX,JUMP
      XI=I-1-ISUB
      H=2.*COS(PIOVM*XI)
      XNORTH=DUMUP+AA*H
      XSOUTH=DUMLO+AA*H
      DEN2=1./XNORTH
      DO 12 J=2,N
 12   W2(J)=POT(I,J-1)+POT(I,J)
      GOTO(201,202),IBCYS
 201  POT(I,1)=W1(2*M1+I)
      GOTO 203
 202  IF(IBCX.EQ.3.OR.IBCX.EQ.4) GOTO 226
C*UL 224  IF(I.EQ.1) GOTO 225
      IF(I.EQ.1) GOTO 225
 226  DEN1=1./(XNORTH+XSOUTH*(1.+.5*COEF2S))
      POT(I,1)=DEN1*(POT(I,1)+.5*XSOUTH*COEF1S*W1(2*M1+I))
      GOTO 203
 225  POT(1,1)=0.
 203  DO 13 J=2,N
 13   POT(I,J)=DEN2*(W2(J)-XSOUTH*POT(I,J-1))
 11   CONTINUE
      IOUT=IOUT+1
      IF(IOUT.EQ.2) GOTO 242
      IF(IBCX.NE.1) GOTO 243
      IMIN=IMAX+1
      IMAX=M
      AA=-1.
      GOTO 241
 243  IF(IBCX.NE.4) GOTO 242
      ISUB=ISUB+1
      IMIN=3
      AA=-1.
      GOTO 241
 242  RETURN
C
C
C   THIS PART OF THE SUBROUTINE IS USED
C   WHEN IKIND=3 THAT IS IN THE HYPERBOLIC CASE
C   AND SOLVES THE THREE-POINT RECURRENCE
C   FORMULA STEP BY STEP
C
C
 300  GOTO(310,320,330,335),IBCX
 310  IMIN=1
      IMAX=M/2+1
      GOTO 340
 320  IMIN=1
      IMAX=M1
      GOTO 340
 330  IMIN=2
      IMAX=M
      GOTO 340
 335  IMIN=2
      IMAX=M1
      JUMP=2
 340  AA=1.
      IOUT=0
      ISUB=0
      DEN1=1./(XSOUTH+XNORTH)
      DEN2=1./XNORTH
 341  DO 7 I=IMIN,IMAX,JUMP
      XI=I-1-ISUB
      H=2.*COS(PIOVM*XI)
      FCENT=CENT-AA*H
      DO 8 J=1,N
 8    W2(J)=POT(I,J)
      POT(I,1)=W1(2*M1+I)
      POT(I,2)=DEN1*(W2(1)+XSOUTH*COEFY*W1(3*M1+I)+FCENT*W1(2*M1+I))
      DO 9 J=3,N
 9    POT(I,J)=DEN2*(W2(J-1)-XSOUTH*POT(I,J-2)+FCENT*POT(I,J-1))
 7    CONTINUE
      IOUT=IOUT+1
      IF(IOUT.EQ.2) GOTO 342
      IF(IBCX.NE.1) GOTO 343
      IMIN=IMAX+1
      IMAX=M
      AA=-1.
      GOTO 341
 343  IF(IBCX.NE.4) GOTO 342
      ISUB=ISUB+1
      IMIN=3
      AA=-1.
      GOTO 341
 342  CONTINUE
      RETURN
      END