csymm.f

贝尔实验室多年开发的矩阵计算程序库的说明文件

      SUBROUTINE CSYMM(SIDE,UPLO,M,N,ALPHA,A,LDA,B,LDB,BETA,C,LDC)
*     .. Scalar Arguments ..
      COMPLEX ALPHA,BETA
      INTEGER LDA,LDB,LDC,M,N
      CHARACTER SIDE,UPLO
*     ..
*     .. Array Arguments ..
      COMPLEX A(LDA,*),B(LDB,*),C(LDC,*)
*     ..
*
*  Purpose
*  =======
*
*  CSYMM  performs one of the matrix-matrix operations
*
*     C := alpha*A*B + beta*C,
*
*  or
*
*     C := alpha*B*A + beta*C,
*
*  where  alpha and beta are scalars, A is a symmetric matrix and  B and
*  C are m by n matrices.
*
*  Arguments
*  ==========
*
*  SIDE   - CHARACTER*1.
*           On entry,  SIDE  specifies whether  the  symmetric matrix  A
*           appears on the  left or right  in the  operation as follows:
*
*              SIDE = 'L' or 'l'   C := alpha*A*B + beta*C,
*
*              SIDE = 'R' or 'r'   C := alpha*B*A + beta*C,
*
*           Unchanged on exit.
*
*  UPLO   - CHARACTER*1.
*           On  entry,   UPLO  specifies  whether  the  upper  or  lower
*           triangular  part  of  the  symmetric  matrix   A  is  to  be
*           referenced as follows:
*
*              UPLO = 'U' or 'u'   Only the upper triangular part of the
*                                  symmetric matrix is to be referenced.
*
*              UPLO = 'L' or 'l'   Only the lower triangular part of the
*                                  symmetric matrix is to be referenced.
*
*           Unchanged on exit.
*
*  M      - INTEGER.
*           On entry,  M  specifies the number of rows of the matrix  C.
*           M  must be at least zero.
*           Unchanged on exit.
*
*  N      - INTEGER.
*           On entry, N specifies the number of columns of the matrix C.
*           N  must be at least zero.
*           Unchanged on exit.
*
*  ALPHA  - COMPLEX         .
*           On entry, ALPHA specifies the scalar alpha.
*           Unchanged on exit.
*
*  A      - COMPLEX          array of DIMENSION ( LDA, ka ), where ka is
*           m  when  SIDE = 'L' or 'l'  and is n  otherwise.
*           Before entry  with  SIDE = 'L' or 'l',  the  m by m  part of
*           the array  A  must contain the  symmetric matrix,  such that
*           when  UPLO = 'U' or 'u', the leading m by m upper triangular
*           part of the array  A  must contain the upper triangular part
*           of the  symmetric matrix and the  strictly  lower triangular
*           part of  A  is not referenced,  and when  UPLO = 'L' or 'l',
*           the leading  m by m  lower triangular part  of the  array  A
*           must  contain  the  lower triangular part  of the  symmetric
*           matrix and the  strictly upper triangular part of  A  is not
*           referenced.
*           Before entry  with  SIDE = 'R' or 'r',  the  n by n  part of
*           the array  A  must contain the  symmetric matrix,  such that
*           when  UPLO = 'U' or 'u', the leading n by n upper triangular
*           part of the array  A  must contain the upper triangular part
*           of the  symmetric matrix and the  strictly  lower triangular
*           part of  A  is not referenced,  and when  UPLO = 'L' or 'l',
*           the leading  n by n  lower triangular part  of the  array  A
*           must  contain  the  lower triangular part  of the  symmetric
*           matrix and the  strictly upper triangular part of  A  is not
*           referenced.
*           Unchanged on exit.
*
*  LDA    - INTEGER.
*           On entry, LDA specifies the first dimension of A as declared
*           in the  calling (sub) program. When  SIDE = 'L' or 'l'  then
*           LDA must be at least  max( 1, m ), otherwise  LDA must be at
*           least max( 1, n ).
*           Unchanged on exit.
*
*  B      - COMPLEX          array of DIMENSION ( LDB, n ).
*           Before entry, the leading  m by n part of the array  B  must
*           contain the matrix B.
*           Unchanged on exit.
*
*  LDB    - INTEGER.
*           On entry, LDB specifies the first dimension of B as declared
*           in  the  calling  (sub)  program.   LDB  must  be  at  least
*           max( 1, m ).
*           Unchanged on exit.
*
*  BETA   - COMPLEX         .
*           On entry,  BETA  specifies the scalar  beta.  When  BETA  is
*           supplied as zero then C need not be set on input.
*           Unchanged on exit.
*
*  C      - COMPLEX          array of DIMENSION ( LDC, n ).
*           Before entry, the leading  m by n  part of the array  C must
*           contain the matrix  C,  except when  beta  is zero, in which
*           case C need not be set on entry.
*           On exit, the array  C  is overwritten by the  m by n updated
*           matrix.
*
*  LDC    - INTEGER.
*           On entry, LDC specifies the first dimension of C as declared
*           in  the  calling  (sub)  program.   LDC  must  be  at  least
*           max( 1, m ).
*           Unchanged on exit.
*
*
*  Level 3 Blas routine.
*
*  -- Written on 8-February-1989.
*     Jack Dongarra, Argonne National Laboratory.
*     Iain Duff, AERE Harwell.
*     Jeremy Du Croz, Numerical Algorithms Group Ltd.
*     Sven Hammarling, Numerical Algorithms Group Ltd.
*
*
*     .. External Functions ..
      LOGICAL LSAME
      EXTERNAL LSAME
*     ..
*     .. External Subroutines ..
      EXTERNAL XERBLA
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC MAX
*     ..
*     .. Local Scalars ..
      COMPLEX TEMP1,TEMP2
      INTEGER I,INFO,J,K,NROWA
      LOGICAL UPPER
*     ..
*     .. Parameters ..
      COMPLEX ONE
      PARAMETER (ONE= (1.0E+0,0.0E+0))
      COMPLEX ZERO
      PARAMETER (ZERO= (0.0E+0,0.0E+0))
*     ..
*
*     Set NROWA as the number of rows of A.
*
      IF (LSAME(SIDE,'L')) THEN
          NROWA = M
      ELSE
          NROWA = N
      END IF
      UPPER = LSAME(UPLO,'U')
*
*     Test the input parameters.
*
      INFO = 0
      IF ((.NOT.LSAME(SIDE,'L')) .AND. (.NOT.LSAME(SIDE,'R'))) THEN
          INFO = 1
      ELSE IF ((.NOT.UPPER) .AND. (.NOT.LSAME(UPLO,'L'))) THEN
          INFO = 2
      ELSE IF (M.LT.0) THEN
          INFO = 3
      ELSE IF (N.LT.0) THEN
          INFO = 4
      ELSE IF (LDA.LT.MAX(1,NROWA)) THEN
          INFO = 7
      ELSE IF (LDB.LT.MAX(1,M)) THEN
          INFO = 9
      ELSE IF (LDC.LT.MAX(1,M)) THEN
          INFO = 12
      END IF
      IF (INFO.NE.0) THEN
          CALL XERBLA('CSYMM ',INFO)
          RETURN
      END IF
*
*     Quick return if possible.
*
      IF ((M.EQ.0) .OR. (N.EQ.0) .OR.
     +    ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN
*
*     And when  alpha.eq.zero.
*
      IF (ALPHA.EQ.ZERO) THEN
          IF (BETA.EQ.ZERO) THEN
              DO 20 J = 1,N
                  DO 10 I = 1,M
                      C(I,J) = ZERO
   10             CONTINUE
   20         CONTINUE
          ELSE
              DO 40 J = 1,N
                  DO 30 I = 1,M
                      C(I,J) = BETA*C(I,J)
   30             CONTINUE
   40         CONTINUE
          END IF
          RETURN
      END IF
*
*     Start the operations.
*
      IF (LSAME(SIDE,'L')) THEN
*
*        Form  C := alpha*A*B + beta*C.
*
          IF (UPPER) THEN
              DO 70 J = 1,N
                  DO 60 I = 1,M
                      TEMP1 = ALPHA*B(I,J)
                      TEMP2 = ZERO
                      DO 50 K = 1,I - 1
                          C(K,J) = C(K,J) + TEMP1*A(K,I)
                          TEMP2 = TEMP2 + B(K,J)*A(K,I)
   50                 CONTINUE
                      IF (BETA.EQ.ZERO) THEN
                          C(I,J) = TEMP1*A(I,I) + ALPHA*TEMP2
                      ELSE
                          C(I,J) = BETA*C(I,J) + TEMP1*A(I,I) +
     +                             ALPHA*TEMP2
                      END IF
   60             CONTINUE
   70         CONTINUE
          ELSE
              DO 100 J = 1,N
                  DO 90 I = M,1,-1
                      TEMP1 = ALPHA*B(I,J)
                      TEMP2 = ZERO
                      DO 80 K = I + 1,M
                          C(K,J) = C(K,J) + TEMP1*A(K,I)
                          TEMP2 = TEMP2 + B(K,J)*A(K,I)
   80                 CONTINUE
                      IF (BETA.EQ.ZERO) THEN
                          C(I,J) = TEMP1*A(I,I) + ALPHA*TEMP2
                      ELSE
                          C(I,J) = BETA*C(I,J) + TEMP1*A(I,I) +
     +                             ALPHA*TEMP2
                      END IF
   90             CONTINUE
  100         CONTINUE
          END IF
      ELSE
*
*        Form  C := alpha*B*A + beta*C.
*
          DO 170 J = 1,N
              TEMP1 = ALPHA*A(J,J)
              IF (BETA.EQ.ZERO) THEN
                  DO 110 I = 1,M
                      C(I,J) = TEMP1*B(I,J)
  110             CONTINUE
              ELSE
                  DO 120 I = 1,M
                      C(I,J) = BETA*C(I,J) + TEMP1*B(I,J)
  120             CONTINUE
              END IF
              DO 140 K = 1,J - 1
                  IF (UPPER) THEN
                      TEMP1 = ALPHA*A(K,J)
                  ELSE
                      TEMP1 = ALPHA*A(J,K)
                  END IF
                  DO 130 I = 1,M
                      C(I,J) = C(I,J) + TEMP1*B(I,K)
  130             CONTINUE
  140         CONTINUE
              DO 160 K = J + 1,N
                  IF (UPPER) THEN
                      TEMP1 = ALPHA*A(J,K)
                  ELSE
                      TEMP1 = ALPHA*A(K,J)
                  END IF
                  DO 150 I = 1,M
                      C(I,J) = C(I,J) + TEMP1*B(I,K)
  150             CONTINUE
  160         CONTINUE
  170     CONTINUE
      END IF
*
      RETURN
*
*     End of CSYMM .
*
      END