SLATEC Routines --- HSTSSP ---
*DECK HSTSSP
SUBROUTINE HSTSSP (A, B, M, MBDCND, BDA, BDB, C, D, N, NBDCND,
+ BDC, BDD, ELMBDA, F, IDIMF, PERTRB, IERROR, W)
C***BEGIN PROLOGUE HSTSSP
C***PURPOSE Solve the standard five-point finite difference
C approximation on a staggered grid to the Helmholtz
C equation in spherical coordinates and on the surface of
C the unit sphere (radius of 1).
C***LIBRARY SLATEC (FISHPACK)
C***CATEGORY I2B1A1A
C***TYPE SINGLE PRECISION (HSTSSP-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 HSTSSP solves the standard five-point finite difference
C approximation on a staggered grid to the Helmholtz equation in
C spherical coordinates and on the surface of the unit sphere
C (radius of 1)
C
C (1/SIN(THETA))(d/dTHETA)(SIN(THETA)(dU/dTHETA)) +
C
C (1/SIN(THETA)**2)(d/dPHI)(dU/dPHI) + LAMBDA*U = F(THETA,PHI)
C
C where THETA is colatitude and PHI is longitude.
C
C * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
C
C * * * * * * * * Parameter Description * * * * * * * * * *
C
C * * * * * * On Input * * * * * *
C
C A,B
C The range of THETA (colatitude), i.e. A .LE. THETA .LE. B. A
C must be less than B and A must be non-negative. A and B are in
C radians. A = 0 corresponds to the north pole and B = PI
C corresponds to the south pole.
C
C
C * * * IMPORTANT * * *
C
C If B is equal to PI, then B must be computed using the statement
C
C B = PIMACH(DUM)
C
C This insures that B in the user's program is equal to PI in this
C program which permits several tests of the input parameters that
C otherwise would not be possible.
C
C * * * * * * * * * * * *
C
C
C
C M
C The number of grid points in the interval (A,B). The grid points
C in the THETA-direction are given by THETA(I) = A + (I-0.5)DTHETA
C for I=1,2,...,M where DTHETA =(B-A)/M. M must be greater than 2.
C
C MBDCND
C Indicates the type of boundary conditions at THETA = A and
C THETA = B.
C
C = 1 If the solution is specified at THETA = A and THETA = B.
C (see note 3 below)
C
C = 2 If the solution is specified at THETA = A and the derivative
C of the solution with respect to THETA is specified at
C THETA = B (see notes 2 and 3 below).
C
C = 3 If the derivative of the solution with respect to THETA is
C specified at THETA = A (see notes 1, 2 below) and THETA = B.
C
C = 4 If the derivative of the solution with respect to THETA is
C specified at THETA = A (see notes 1 and 2 below) and the
C solution is specified at THETA = B.
C
C = 5 If the solution is unspecified at THETA = A = 0 and the
C solution is specified at THETA = B. (see note 3 below)
C
C = 6 If the solution is unspecified at THETA = A = 0 and the
C derivative of the solution with respect to THETA is
C specified at THETA = B (see note 2 below).
C
C = 7 If the solution is specified at THETA = A and the
C solution is unspecified at THETA = B = PI. (see note 3 below)
C
C = 8 If the derivative of the solution with respect to
C THETA is specified at THETA = A (see note 1 below)
C and the solution is unspecified at THETA = B = PI.
C
C = 9 If the solution is unspecified at THETA = A = 0 and
C THETA = B = PI.
C
C NOTES: 1. If A = 0, do not use MBDCND = 3, 4, or 8,
C but instead use MBDCND = 5, 6, or 9.
C
C 2. If B = PI, do not use MBDCND = 2, 3, or 6,
C but instead use MBDCND = 7, 8, or 9.
C
C 3. When the solution is specified at THETA = 0 and/or
C THETA = PI and the other boundary conditions are
C combinations of unspecified, normal derivative, or
C periodicity a singular system results. The unique
C solution is determined by extrapolation to the
C specification of the solution at either THETA = 0 or
C THETA = PI. But in these cases the right side of the
C system will be perturbed by the constant PERTRB.
C
C BDA
C A one-dimensional array of length N that specifies the boundary
C values (if any) of the solution at THETA = A. When
C MBDCND = 1, 2, or 7,
C
C BDA(J) = U(A,PHI(J)) , J=1,2,...,N.
C
C When MBDCND = 3, 4, or 8,
C
C BDA(J) = (d/dTHETA)U(A,PHI(J)) , J=1,2,...,N.
C
C When MBDCND has any other value, BDA is a dummy variable.
C
C BDB
C A one-dimensional array of length N that specifies the boundary
C values of the solution at THETA = B. When MBDCND = 1,4, or 5,
C
C BDB(J) = U(B,PHI(J)) , J=1,2,...,N.
C
C When MBDCND = 2,3, or 6,
C
C BDB(J) = (d/dTHETA)U(B,PHI(J)) , J=1,2,...,N.
C
C When MBDCND has any other value, BDB is a dummy variable.
C
C C,D
C The range of PHI (longitude), i.e. C .LE. PHI .LE. D.
C C must be less than D. If D-C = 2*PI, periodic boundary
C conditions are usually prescribed.
C
C N
C The number of unknowns in the interval (C,D). The unknowns in
C the PHI-direction are given by PHI(J) = C + (J-0.5)DPHI,
C J=1,2,...,N, where DPHI = (D-C)/N. N must be greater than 2.
C
C NBDCND
C Indicates the type of boundary conditions at PHI = C
C and PHI = D.
C
C = 0 If the solution is periodic in PHI, i.e.
C U(I,J) = U(I,N+J).
C
C = 1 If the solution is specified at PHI = C and PHI = D
C (see note below).
C
C = 2 If the solution is specified at PHI = C and the derivative
C of the solution with respect to PHI is specified at
C PHI = D (see note below).
C
C = 3 If the derivative of the solution with respect to PHI is
C specified at PHI = C and PHI = D.
C
C = 4 If the derivative of the solution with respect to PHI is
C specified at PHI = C and the solution is specified at
C PHI = D (see note below).
C
C NOTE: When NBDCND = 1, 2, or 4, do not use MBDCND = 5, 6, 7, 8,
C or 9 (the former indicates that the solution is specified at
C a pole; the latter indicates the solution is unspecified). Use
C instead MBDCND = 1 or 2.
C
C BDC
C A one dimensional array of length M that specifies the boundary
C values of the solution at PHI = C. When NBDCND = 1 or 2,
C
C BDC(I) = U(THETA(I),C) , I=1,2,...,M.
C
C When NBDCND = 3 or 4,
C
C BDC(I) = (d/dPHI)U(THETA(I),C), I=1,2,...,M.
C
C When NBDCND = 0, BDC is a dummy variable.
C
C BDD
C A one-dimensional array of length M that specifies the boundary
C values of the solution at PHI = D. When NBDCND = 1 or 4,
C
C BDD(I) = U(THETA(I),D) , I=1,2,...,M.
C
C When NBDCND = 2 or 3,
C
C BDD(I) = (d/dPHI)U(THETA(I),D) , I=1,2,...,M.
C
C When NBDCND = 0, BDD is a dummy variable.
C
C ELMBDA
C The constant LAMBDA in the Helmholtz equation. If LAMBDA is
C greater than 0, a solution may not exist. However, HSTSSP will
C attempt to find a solution.
C
C F
C A two-dimensional array that specifies the values of the right
C side of the Helmholtz equation. For I=1,2,...,M and J=1,2,...,N
C
C F(I,J) = F(THETA(I),PHI(J)) .
C
C F must be dimensioned at least M X N.
C
C IDIMF
C The row (or first) dimension of the array F as it appears in the
C program calling HSTSSP. This parameter is used to specify the
C variable dimension of F. IDIMF must be at least M.
C
C W
C A one-dimensional array that must be provided by the user for
C work space. W may require up to 13M + 4N + M*INT(log2(N))
C locations. The actual number of locations used is computed by
C HSTSSP and is returned in the location W(1).
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)) for
C I=1,2,...,M, J=1,2,...,N.
C
C PERTRB
C If a combination of periodic, derivative, or unspecified
C boundary conditions is specified for a Poisson equation
C (LAMBDA = 0), a solution may not exist. PERTRB is a con-
C stant, calculated and subtracted from F, which ensures
C that a solution exists. HSTSSP then computes this
C solution, which is a least squares solution to the
C original approximation. This solution plus any constant is also
C a solution; hence, the solution is not unique. The value of
C PERTRB should be small compared to the right side F.
C Otherwise, a solution is obtained to an essentially different
C problem. This comparison should always be made to insure that
C a meaningful solution has been obtained.
C
C IERROR
C An error flag that indicates invalid input parameters.
C Except for numbers 0 and 14, a solution is not attempted.
C
C = 0 No error
C
C = 1 A .LT. 0 or B .GT. PI
C
C = 2 A .GE. B
C
C = 3 MBDCND .LT. 1 or MBDCND .GT. 9
C
C = 4 C .GE. D
C
C = 5 N .LE. 2
C
C = 6 NBDCND .LT. 0 or NBDCND .GT. 4
C
C = 7 A .GT. 0 and MBDCND = 5, 6, or 9
C
C = 8 A = 0 and MBDCND = 3, 4, or 8
C
C = 9 B .LT. PI and MBDCND .GE. 7
C
C = 10 B = PI and MBDCND = 2,3, or 6
C
C = 11 MBDCND .GE. 5 and NDBCND = 1, 2, or 4
C
C = 12 IDIMF .LT. M
C
C = 13 M .LE. 2
C
C = 14 LAMBDA .GT. 0
C
C Since this is the only means of indicating a possibly
C incorrect call to HSTSSP, the user should test IERROR after
C the call.
C
C W
C W(1) contains the required length of W.
C
C *Long Description:
C
C * * * * * * * Program Specifications * * * * * * * * * * * *
C
C Dimension of BDA(N),BDB(N),BDC(M),BDD(M),F(IDIMF,N),
C Arguments W(see argument list)
C
C Latest June 1, 1977
C Revision
C
C Subprograms HSTSSP,POISTG,POSTG2,GENBUN,POISD2,POISN2,POISP2,
C Required COSGEN,MERGE,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 Roland Sweet
C
C Language FORTRAN
C
C History Written by Roland Sweet at NCAR in April, 1977
C
C Algorithm This subroutine defines the finite-difference
C equations, incorporates boundary data, adjusts the
C right side when the system is singular and calls
C either POISTG or GENBUN which solves the linear
C system of equations.
C
C Space 8427(decimal) = 20353(octal) locations on the
C Required NCAR Control Data 7600
C
C Timing and The execution time T on the NCAR Control Data
C Accuracy 7600 for subroutine HSTSSP is roughly proportional
C to M*N*log2(N). Some typical values are listed in
C the table below.
C The solution process employed results in a loss
C of no more than four significant digits for N and M
C as large as 64. More detailed information about
C accuracy can be found in the documentation for
C subroutine POISTG which is the routine that
C actually solves the finite difference equations.
C
C
C M(=N) MBDCND NBDCND T(MSECS)
C ----- ------ ------ --------
C
C 32 1-9 1-4 56
C 64 1-9 1-4 230
C
C Portability American National Standards Institute FORTRAN.
C The machine dependent constant PI is defined in
C function PIMACH.
C
C Required COS
C Resident
C Routines
C
C Reference Schumann, U. and R. Sweet,'A Direct Method For
C The Solution Of Poisson's Equation With Neumann
C Boundary Conditions On A Staggered Grid Of
C Arbitrary Size,' J. Comp. Phys. 20(1976),
C pp. 171-182.
C
C * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
C
C***REFERENCES U. Schumann and R. Sweet, A direct method for the
C solution of Poisson's equation with Neumann boundary
C conditions on a staggered grid of arbitrary size,
C Journal of Computational Physics 20, (1976),
C pp. 171-182.
C***ROUTINES CALLED GENBUN, PIMACH, POISTG
C***REVISION HISTORY (YYMMDD)
C 801001 DATE WRITTEN
C 890531 Changed all specific intrinsics to generic. (WRB)
C 890531 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 HSTSSP