*DECK HWSSSP
SUBROUTINE HWSSSP (TS, TF, M, MBDCND, BDTS, BDTF, PS, PF, N,
+ NBDCND, BDPS, BDPF, ELMBDA, F, IDIMF, PERTRB, IERROR, W)
C***BEGIN PROLOGUE HWSSSP
C***PURPOSE Solve a finite difference approximation to the Helmholtz
C equation in spherical coordinates and on the surface of the
C unit sphere (radius of 1).
C***LIBRARY SLATEC (FISHPACK)
C***CATEGORY I2B1A1A
C***TYPE SINGLE PRECISION (HWSSSP-S)
C***KEYWORDS ELLIPTIC, FISHPACK, HELMHOLTZ, PDE, SPHERICAL
C***AUTHOR Adams, J., (NCAR)
C Swarztrauber, P. N., (NCAR)
C Sweet, R., (NCAR)
C***DESCRIPTION
C
C Subroutine HWSSSP solves a finite difference approximation to the
C Helmholtz equation in spherical coordinates and on the surface of
C the unit sphere (radius of 1):
C
C (1/SIN(THETA))(d/dTHETA)(SIN(THETA)(dU/dTHETA))
C
C + (1/SIN(THETA)**2)(d/dPHI)(dU/dPHI)
C
C + LAMBDA*U = F(THETA,PHI)
C
C Where THETA is colatitude and PHI is longitude.
C
C * * * * * * * * Parameter Description * * * * * * * * * *
C
C * * * * * * On Input * * * * * *
C
C TS,TF
C The range of THETA (colatitude), i.e., TS .LE. THETA .LE. TF.
C TS must be less than TF. TS and TF are in radians. A TS of
C zero corresponds to the north pole and a TF of PI corresponds to
C the south pole.
C
C * * * * * * * * * * * * * * IMPORTANT * * * * * * * * * * * * * *
C
C If TF is equal to PI then it must be computed using the statement
C TF = PIMACH(DUM). This insures that TF in the users program is
C equal to PI in this program which permits several tests of the
C input parameters that otherwise would not be possible.
C
C
C M
C The number of panels into which the interval (TS,TF) is
C subdivided. Hence, there will be M+1 grid points in the
C THETA-direction given by THETA(I) = (I-1)DTHETA+TS for
C I = 1,2,...,M+1, where DTHETA = (TF-TS)/M is the panel width.
C M must be greater than 5.
C
C MBDCND
C Indicates the type of boundary condition at THETA = TS and
C THETA = TF.
C
C = 1 If the solution is specified at THETA = TS and THETA = TF.
C = 2 If the solution is specified at THETA = TS and the
C derivative of the solution with respect to THETA is
C specified at THETA = TF (see note 2 below).
C = 3 If the derivative of the solution with respect to THETA is
C specified at THETA = TS and THETA = TF (see notes 1,2
C below).
C = 4 If the derivative of the solution with respect to THETA is
C specified at THETA = TS (see note 1 below) and the
C solution is specified at THETA = TF.
C = 5 If the solution is unspecified at THETA = TS = 0 and the
C solution is specified at THETA = TF.
C = 6 If the solution is unspecified at THETA = TS = 0 and the
C derivative of the solution with respect to THETA is
C specified at THETA = TF (see note 2 below).
C = 7 If the solution is specified at THETA = TS and the
C solution is unspecified at THETA = TF = PI.
C = 8 If the derivative of the solution with respect to THETA is
C specified at THETA = TS (see note 1 below) and the
C solution is unspecified at THETA = TF = PI.
C = 9 If the solution is unspecified at THETA = TS = 0 and
C THETA = TF = PI.
C
C NOTES: 1. If TS = 0, do not use MBDCND = 3,4, or 8, but
C instead use MBDCND = 5,6, or 9 .
C 2. If TF = PI, do not use MBDCND = 2,3, or 6, but
C instead use MBDCND = 7,8, or 9 .
C
C BDTS
C A one-dimensional array of length N+1 that specifies the values
C of the derivative of the solution with respect to THETA at
C THETA = TS. When MBDCND = 3,4, or 8,
C
C BDTS(J) = (d/dTHETA)U(TS,PHI(J)), J = 1,2,...,N+1 .
C
C When MBDCND has any other value, BDTS is a dummy variable.
C
C BDTF
C A one-dimensional array of length N+1 that specifies the values
C of the derivative of the solution with respect to THETA at
C THETA = TF. When MBDCND = 2,3, or 6,
C
C BDTF(J) = (d/dTHETA)U(TF,PHI(J)), J = 1,2,...,N+1 .
C
C When MBDCND has any other value, BDTF is a dummy variable.
C
C PS,PF
C The range of PHI (longitude), i.e., PS .LE. PHI .LE. PF. PS
C must be less than PF. PS and PF are in radians. If PS = 0 and
C PF = 2*PI, periodic boundary conditions are usually prescribed.
C
C * * * * * * * * * * * * * * IMPORTANT * * * * * * * * * * * * * *
C
C If PF is equal to 2*PI then it must be computed using the
C statement PF = 2.*PIMACH(DUM). This insures that PF in the users
C program is equal to 2*PI in this program which permits tests of
C the input parameters that otherwise would not be possible.
C
C
C N
C The number of panels into which the interval (PS,PF) is
C subdivided. Hence, there will be N+1 grid points in the
C PHI-direction given by PHI(J) = (J-1)DPHI+PS for
C J = 1,2,...,N+1, where DPHI = (PF-PS)/N is the panel width.
C N must be greater than 4.
C
C NBDCND
C Indicates the type of boundary condition at PHI = PS and
C PHI = PF.
C
C = 0 If the solution is periodic in PHI, i.e.,
C U(I,J) = U(I,N+J).
C = 1 If the solution is specified at PHI = PS and PHI = PF
C (see note below).
C = 2 If the solution is specified at PHI = PS (see note below)
C and the derivative of the solution with respect to PHI is
C specified at PHI = PF.
C = 3 If the derivative of the solution with respect to PHI is
C specified at PHI = PS and PHI = PF.
C = 4 If the derivative of the solution with respect to PHI is
C specified at PS and the solution is specified at PHI = PF
C (see note below).
C
C NOTE: NBDCND = 1,2, or 4 cannot be used with
C MBDCND = 5,6,7,8, or 9 (the former indicates that the
C solution is specified at a pole, the latter
C indicates that the solution is unspecified).
C Use instead
C MBDCND = 1 or 2 .
C
C BDPS
C A one-dimensional array of length M+1 that specifies the values
C of the derivative of the solution with respect to PHI at
C PHI = PS. When NBDCND = 3 or 4,
C
C BDPS(I) = (d/dPHI)U(THETA(I),PS), I = 1,2,...,M+1 .
C
C When NBDCND has any other value, BDPS is a dummy variable.
C
C BDPF
C A one-dimensional array of length M+1 that specifies the values
C of the derivative of the solution with respect to PHI at
C PHI = PF. When NBDCND = 2 or 3,
C
C BDPF(I) = (d/dPHI)U(THETA(I),PF), I = 1,2,...,M+1 .
C
C When NBDCND has any other value, BDPF is a dummy variable.
C
C ELMBDA
C The constant LAMBDA in the Helmholtz equation. If
C LAMBDA .GT. 0, a solution may not exist. However, HWSSSP will
C attempt to find a solution.
C
C F
C A two-dimensional array that specifies the value of the right
C side of the Helmholtz equation and boundary values (if any).
C For I = 2,3,...,M and J = 2,3,...,N
C
C F(I,J) = F(THETA(I),PHI(J)).
C
C On the boundaries F is defined by
C
C MBDCND F(1,J) F(M+1,J)
C ------ ------------ ------------
C
C 1 U(TS,PHI(J)) U(TF,PHI(J))
C 2 U(TS,PHI(J)) F(TF,PHI(J))
C 3 F(TS,PHI(J)) F(TF,PHI(J))
C 4 F(TS,PHI(J)) U(TF,PHI(J))
C 5 F(0,PS) U(TF,PHI(J)) J = 1,2,...,N+1
C 6 F(0,PS) F(TF,PHI(J))
C 7 U(TS,PHI(J)) F(PI,PS)
C 8 F(TS,PHI(J)) F(PI,PS)
C 9 F(0,PS) F(PI,PS)
C
C NBDCND F(I,1) F(I,N+1)
C ------ -------------- --------------
C
C 0 F(THETA(I),PS) F(THETA(I),PS)
C 1 U(THETA(I),PS) U(THETA(I),PF)
C 2 U(THETA(I),PS) F(THETA(I),PF) I = 1,2,...,M+1
C 3 F(THETA(I),PS) F(THETA(I),PF)
C 4 F(THETA(I),PS) U(THETA(I),PF)
C
C F must be dimensioned at least (M+1)*(N+1).
C
C *NOTE*
C
C If the table calls for both the solution U and the right side F
C at a corner then the solution must be specified.
C
C
C IDIMF
C The row (or first) dimension of the array F as it appears in the
C program calling HWSSSP. This parameter is used to specify the
C variable dimension of F. IDIMF must be at least M+1 .
C
C W
C A one-dimensional array that must be provided by the user for
C work space. W may require up to 4*(N+1)+(16+INT(log2(N+1)))(M+1)
C locations. The actual number of locations used is computed by
C HWSSSP and is output in location W(1). INT( ) denotes the
C FORTRAN integer function.
C
C
C * * * * * * * * * * On Output * * * * * * * * * *
C
C F
C Contains the solution U(I,J) of the finite difference
C approximation for the grid point (THETA(I),PHI(J)),
C I = 1,2,...,M+1, J = 1,2,...,N+1 .
C
C PERTRB
C If one specifies a combination of periodic, derivative or
C unspecified boundary conditions for a Poisson equation
C (LAMBDA = 0), a solution may not exist. PERTRB is a constant,
C calculated and subtracted from F, which ensures that a solution
C exists. HWSSSP then computes this solution, which is a least
C squares solution to the original approximation. This solution
C is not unique and is unnormalized. The value of PERTRB should
C be small compared to the right side F. Otherwise , a solution
C is obtained to an essentially different problem. This comparison
C should always be made to insure that a meaningful solution has
C been obtained.
C
C IERROR
C An error flag that indicates invalid input parameters. Except
C for numbers 0 and 8, a solution is not attempted.
C
C = 0 No error
C = 1 TS.LT.0 or TF.GT.PI
C = 2 TS.GE.TF
C = 3 MBDCND.LT.1 or MBDCND.GT.9
C = 4 PS.LT.0 or PS.GT.PI+PI
C = 5 PS.GE.PF
C = 6 N.LT.5
C = 7 M.LT.5
C = 8 NBDCND.LT.0 or NBDCND.GT.4
C = 9 ELMBDA.GT.0
C = 10 IDIMF.LT.M+1
C = 11 NBDCND equals 1,2 or 4 and MBDCND.GE.5
C = 12 TS.EQ.0 and MBDCND equals 3,4 or 8
C = 13 TF.EQ.PI and MBDCND equals 2,3 or 6
C = 14 MBDCND equals 5,6 or 9 and TS.NE.0
C = 15 MBDCND.GE.7 and TF.NE.PI
C
C Since this is the only means of indicating a possibly incorrect
C call to HWSSSP, the user should test IERROR after a call.
C
C W
C Contains intermediate values that must not be destroyed if
C HWSSSP will be called again with INTL = 1. W(1) contains the
C required length of W .
C
C *Long Description:
C
C * * * * * * * Program Specifications * * * * * * * * * * * *
C
C Dimension of BDTS(N+1),BDTF(N+1),BDPS(M+1),BDPF(M+1),
C Arguments F(IDIMF,N+1),W(see argument list)
C
C Latest January 1978
C Revision
C
C
C Subprograms HWSSSP,HWSSS1,GENBUN,POISD2,POISN2,POISP2,COSGEN,ME
C Required TRIX,TRI3,PIMACH
C
C Special NONE
C Conditions
C
C Common NONE
C Blocks
C
C I/O NONE
C
C Precision Single
C
C Specialist Paul Swarztrauber
C
C Language FORTRAN
C
C History Version 1 - September 1973
C Version 2 - April 1976
C Version 3 - January 1978
C
C Algorithm The routine defines the finite difference
C equations, incorporates boundary data, and adjusts
C the right side of singular systems and then calls
C GENBUN to solve the system.
C
C Space
C Required CONTROL DATA 7600
C
C Timing and The execution time T on the NCAR Control Data
C Accuracy 7600 for subroutine HWSSSP is roughly proportional
C to M*N*log2(N), but also depends on the input
C parameters NBDCND and MBDCND. Some typical values
C are listed in the table below.
C The solution process employed results in a loss
C of no more than three significant digits for N and
C M as large as 64. More detailed information about
C accuracy can be found in the documentation for
C subroutine GENBUN which is the routine that
C solves the finite difference equations.
C
C
C M(=N) MBDCND NBDCND T(MSECS)
C ----- ------ ------ --------
C
C 32 0 0 31
C 32 1 1 23
C 32 3 3 36
C 64 0 0 128
C 64 1 1 96
C 64 3 3 142
C
C Portability American National Standards Institute FORTRAN.
C The machine dependent constant PI is defined in
C function PIMACH.
C
C Required SIN,COS
C Resident
C Routines
C
C References P. N. Swarztrauber,'The Direct Solution Of The
C Discrete Poisson Equation On The Surface Of a
C Sphere, SIAM J. Numer. Anal.,15(1974), pp 212-215
C
C Swarztrauber,P. and R. Sweet, 'Efficient FORTRAN
C Subprograms for The Solution of Elliptic Equations'
C NCAR TN/IA-109, July, 1975, 138 pp.
C
C * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
C
C***REFERENCES P. N. Swarztrauber and R. Sweet, Efficient Fortran
C subprograms for the solution of elliptic equations,
C NCAR TN/IA-109, July 1975, 138 pp.
C P. N. Swarztrauber, The direct solution of the discrete
C Poisson equation on the surface of a sphere, SIAM
C Journal on Numerical Analysis 15 (1974), pp. 212-215.
C***ROUTINES CALLED HWSSS1, PIMACH
C***REVISION HISTORY (YYMMDD)
C 801001 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 891009 Removed unreferenced variable. (WRB)
C 891009 REVISION DATE from Version 3.2
C 891214 Prologue converted to Version 4.0 format. (BAB)
C 920501 Reformatted the REFERENCES section. (WRB)
C***END PROLOGUE HWSSSP
C
DIMENSION F(IDIMF,*) ,BDTS(*) ,BDTF(*) ,BDPS(*) ,
1 BDPF(*) ,W(*)
C***FIRST EXECUTABLE STATEMENT HWSSSP
PI = PIMACH(DUM)
TPI = 2.*PI
IERROR = 0
IF (TS.LT.0. .OR. TF.GT.PI) IERROR = 1
IF (TS .GE. TF) IERROR = 2
IF (MBDCND.LT.1 .OR. MBDCND.GT.9) IERROR = 3
IF (PS.LT.0. .OR. PF.GT.TPI) IERROR = 4
IF (PS .GE. PF) IERROR = 5
IF (N .LT. 5) IERROR = 6
IF (M .LT. 5) IERROR = 7
IF (NBDCND.LT.0 .OR. NBDCND.GT.4) IERROR = 8
IF (ELMBDA .GT. 0.) IERROR = 9
IF (IDIMF .LT. M+1) IERROR = 10
IF ((NBDCND.EQ.1 .OR. NBDCND.EQ.2 .OR. NBDCND.EQ.4) .AND.
1 MBDCND.GE.5) IERROR = 11
IF (TS.EQ.0. .AND.
1 (MBDCND.EQ.3 .OR. MBDCND.EQ.4 .OR. MBDCND.EQ.8)) IERROR = 12
IF (TF.EQ.PI .AND.
1 (MBDCND.EQ.2 .OR. MBDCND.EQ.3 .OR. MBDCND.EQ.6)) IERROR = 13
IF ((MBDCND.EQ.5 .OR. MBDCND.EQ.6 .OR. MBDCND.EQ.9) .AND.
1 TS.NE.0.) IERROR = 14
IF (MBDCND.GE.7 .AND. TF.NE.PI) IERROR = 15
IF (IERROR.NE.0 .AND. IERROR.NE.9) RETURN
CALL HWSSS1 (TS,TF,M,MBDCND,BDTS,BDTF,PS,PF,N,NBDCND,BDPS,BDPF,
1 ELMBDA,F,IDIMF,PERTRB,W,W(M+2),W(2*M+3),W(3*M+4),
2 W(4*M+5),W(5*M+6),W(6*M+7))
W(1) = W(6*M+7)+6*(M+1)
RETURN
END