Solving Partial Differential Equation Applications with PDE2D

Appendix DProblem 5.7 Local Solvers

D.1 DTD3M,DTD3N,DCG (problem57.f)

- - - - - - DTD3M - - - - - - - - - - - -

      SUBROUTINE DTD3M(N,NZ,IR,IC,A,B,JOB,SPD)
      IMPLICIT DOUBLE PRECISION (A-H,O-Z)
      DIMENSION IR(NZ),IC(NZ),A(NZ),B(N)
      LOGICAL SPD
      COMMON /DTDP27/ ITASK,NPES,ICOMM
C
C  DTD3M IS A LOCALLY-WRITTEN CODE WHICH SOLVES A SPARSE SYMMETRIC
C  LINEAR SYSTEM A*X=B.  IT WILL BE CALLED WHEN ISOLVE=5 FOR A SYMMETRIC
C  2D GALERKIN PROBLEM, AND WHEN ISOLVE=4 FOR A 2D OR 3D COLLOCATION PROBLEM.
C  IF YOU ACTIVATE DTD3M,DTD3N, YOU SHOULD ALSO INCREASE ISMX2D AND ISMX3D TO
C  AT LEAST 5 IN THE FILE 'pde2d.f'.
C
C  N  - NUMBER OF EQUATIONS AND UNKNOWNS (INPUT)
C  NZ - NUMBER OF NONZEROS IN THE UPPER TRIANGLE OF A (INPUT)
C  IR - ROW NUMBERS OF THE NONZEROS IN THE UPPER TRIANGLE OF A (INPUT)
C  IC - COLUMN NUMBERS OF THE NONZEROS IN THE UPPER TRIANGLE OF A (INPUT)
C  A  - NONZERO ELEMENTS OF THE UPPER TRIANGLE OF A (INPUT).  A(J)
C         CONTAINS ELEMENT (IR(J),IC(J)), J=1,...,NZ, OF THE MATRIX,
C         WHERE IC(J).GE.IR(J).
C  B  - ON INPUT, B WILL CONTAIN THE RIGHT HAND SIDE OF THE LINEAR
C         SYSTEM.  ON OUTPUT, B SHOULD CONTAIN THE SOLUTION, X.
C  JOB- JOB PARAMETER (INPUT).  IF JOB=2, THIS MEANS THAT THE MATRIX
C         A HAS CHANGED SINCE THE LAST CALL TO DTD3M, WHILE JOB=3 MEANS
C         A HAS NOT CHANGED.  THUS, IF YOU WISH, YOU CAN COMPUTE AN LU
C         DECOMPOSITION OF A WHEN JOB=2 AND SAVE IT, AND USE THIS
C         DECOMPOSITION TO SOLVE THE SYSTEM MORE RAPIDLY, WHEN JOB=3.
C SPD- .TRUE. IF LINEAR SYSTEM IS POSITIVE DEFINITE. (INPUT) ...