LAPACK: BLAS/SRC/zgemv.f Source File

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00001       SUBROUTINE ZGEMV(TRANS,M,N,ALPHA,A,LDA,X,INCX,BETA,Y,INCY)
00002 *     .. Scalar Arguments ..
00003       DOUBLE COMPLEX ALPHA,BETA
00004       INTEGER INCX,INCY,LDA,M,N
00005       CHARACTER TRANS
00006 *     ..
00007 *     .. Array Arguments ..
00008       DOUBLE COMPLEX A(LDA,*),X(*),Y(*)
00009 *     ..
00010 *
00011 *  Purpose
00012 *  =======
00013 *
00014 *  ZGEMV  performs one of the matrix-vector operations
00015 *
00016 *     y := alpha*A*x + beta*y,   or   y := alpha*A'*x + beta*y,   or
00017 *
00018 *     y := alpha*conjg( A' )*x + beta*y,
00019 *
00020 *  where alpha and beta are scalars, x and y are vectors and A is an
00021 *  m by n matrix.
00022 *
00023 *  Arguments
00024 *  ==========
00025 *
00026 *  TRANS  - CHARACTER*1.
00027 *           On entry, TRANS specifies the operation to be performed as
00028 *           follows:
00029 *
00030 *              TRANS = 'N' or 'n'   y := alpha*A*x + beta*y.
00031 *
00032 *              TRANS = 'T' or 't'   y := alpha*A'*x + beta*y.
00033 *
00034 *              TRANS = 'C' or 'c'   y := alpha*conjg( A' )*x + beta*y.
00035 *
00036 *           Unchanged on exit.
00037 *
00038 *  M      - INTEGER.
00039 *           On entry, M specifies the number of rows of the matrix A.
00040 *           M must be at least zero.
00041 *           Unchanged on exit.
00042 *
00043 *  N      - INTEGER.
00044 *           On entry, N specifies the number of columns of the matrix A.
00045 *           N must be at least zero.
00046 *           Unchanged on exit.
00047 *
00048 *  ALPHA  - COMPLEX*16      .
00049 *           On entry, ALPHA specifies the scalar alpha.
00050 *           Unchanged on exit.
00051 *
00052 *  A      - COMPLEX*16       array of DIMENSION ( LDA, n ).
00053 *           Before entry, the leading m by n part of the array A must
00054 *           contain the matrix of coefficients.
00055 *           Unchanged on exit.
00056 *
00057 *  LDA    - INTEGER.
00058 *           On entry, LDA specifies the first dimension of A as declared
00059 *           in the calling (sub) program. LDA must be at least
00060 *           max( 1, m ).
00061 *           Unchanged on exit.
00062 *
00063 *  X      - COMPLEX*16       array of DIMENSION at least
00064 *           ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n'
00065 *           and at least
00066 *           ( 1 + ( m - 1 )*abs( INCX ) ) otherwise.
00067 *           Before entry, the incremented array X must contain the
00068 *           vector x.
00069 *           Unchanged on exit.
00070 *
00071 *  INCX   - INTEGER.
00072 *           On entry, INCX specifies the increment for the elements of
00073 *           X. INCX must not be zero.
00074 *           Unchanged on exit.
00075 *
00076 *  BETA   - COMPLEX*16      .
00077 *           On entry, BETA specifies the scalar beta. When BETA is
00078 *           supplied as zero then Y need not be set on input.
00079 *           Unchanged on exit.
00080 *
00081 *  Y      - COMPLEX*16       array of DIMENSION at least
00082 *           ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n'
00083 *           and at least
00084 *           ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.
00085 *           Before entry with BETA non-zero, the incremented array Y
00086 *           must contain the vector y. On exit, Y is overwritten by the
00087 *           updated vector y.
00088 *
00089 *  INCY   - INTEGER.
00090 *           On entry, INCY specifies the increment for the elements of
00091 *           Y. INCY must not be zero.
00092 *           Unchanged on exit.
00093 *
00094 *  Further Details
00095 *  ===============
00096 *
00097 *  Level 2 Blas routine.
00098 *
00099 *  -- Written on 22-October-1986.
00100 *     Jack Dongarra, Argonne National Lab.
00101 *     Jeremy Du Croz, Nag Central Office.
00102 *     Sven Hammarling, Nag Central Office.
00103 *     Richard Hanson, Sandia National Labs.
00104 *
00105 *  =====================================================================
00106 *
00107 *     .. Parameters ..
00108       DOUBLE COMPLEX ONE
00109       PARAMETER (ONE= (1.0D+0,0.0D+0))
00110       DOUBLE COMPLEX ZERO
00111       PARAMETER (ZERO= (0.0D+0,0.0D+0))
00112 *     ..
00113 *     .. Local Scalars ..
00114       DOUBLE COMPLEX TEMP
00115       INTEGER I,INFO,IX,IY,J,JX,JY,KX,KY,LENX,LENY
00116       LOGICAL NOCONJ
00117 *     ..
00118 *     .. External Functions ..
00119       LOGICAL LSAME
00120       EXTERNAL LSAME
00121 *     ..
00122 *     .. External Subroutines ..
00123       EXTERNAL XERBLA
00124 *     ..
00125 *     .. Intrinsic Functions ..
00126       INTRINSIC DCONJG,MAX
00127 *     ..
00128 *
00129 *     Test the input parameters.
00130 *
00131       INFO = 0
00132       IF (.NOT.LSAME(TRANS,'N') .AND. .NOT.LSAME(TRANS,'T') .AND.
00133      +    .NOT.LSAME(TRANS,'C')) THEN
00134           INFO = 1
00135       ELSE IF (M.LT.0) THEN
00136           INFO = 2
00137       ELSE IF (N.LT.0) THEN
00138           INFO = 3
00139       ELSE IF (LDA.LT.MAX(1,M)) THEN
00140           INFO = 6
00141       ELSE IF (INCX.EQ.0) THEN
00142           INFO = 8
00143       ELSE IF (INCY.EQ.0) THEN
00144           INFO = 11
00145       END IF
00146       IF (INFO.NE.0) THEN
00147           CALL XERBLA('ZGEMV ',INFO)
00148           RETURN
00149       END IF
00150 *
00151 *     Quick return if possible.
00152 *
00153       IF ((M.EQ.0) .OR. (N.EQ.0) .OR.
00154      +    ((ALPHA.EQ.ZERO).AND. (BETA.EQ.ONE))) RETURN
00155 *
00156       NOCONJ = LSAME(TRANS,'T')
00157 *
00158 *     Set  LENX  and  LENY, the lengths of the vectors x and y, and set
00159 *     up the start points in  X  and  Y.
00160 *
00161       IF (LSAME(TRANS,'N')) THEN
00162           LENX = N
00163           LENY = M
00164       ELSE
00165           LENX = M
00166           LENY = N
00167       END IF
00168       IF (INCX.GT.0) THEN
00169           KX = 1
00170       ELSE
00171           KX = 1 - (LENX-1)*INCX
00172       END IF
00173       IF (INCY.GT.0) THEN
00174           KY = 1
00175       ELSE
00176           KY = 1 - (LENY-1)*INCY
00177       END IF
00178 *
00179 *     Start the operations. In this version the elements of A are
00180 *     accessed sequentially with one pass through A.
00181 *
00182 *     First form  y := beta*y.
00183 *
00184       IF (BETA.NE.ONE) THEN
00185           IF (INCY.EQ.1) THEN
00186               IF (BETA.EQ.ZERO) THEN
00187                   DO 10 I = 1,LENY
00188                       Y(I) = ZERO
00189    10             CONTINUE
00190               ELSE
00191                   DO 20 I = 1,LENY
00192                       Y(I) = BETA*Y(I)
00193    20             CONTINUE
00194               END IF
00195           ELSE
00196               IY = KY
00197               IF (BETA.EQ.ZERO) THEN
00198                   DO 30 I = 1,LENY
00199                       Y(IY) = ZERO
00200                       IY = IY + INCY
00201    30             CONTINUE
00202               ELSE
00203                   DO 40 I = 1,LENY
00204                       Y(IY) = BETA*Y(IY)
00205                       IY = IY + INCY
00206    40             CONTINUE
00207               END IF
00208           END IF
00209       END IF
00210       IF (ALPHA.EQ.ZERO) RETURN
00211       IF (LSAME(TRANS,'N')) THEN
00212 *
00213 *        Form  y := alpha*A*x + y.
00214 *
00215           JX = KX
00216           IF (INCY.EQ.1) THEN
00217               DO 60 J = 1,N
00218                   IF (X(JX).NE.ZERO) THEN
00219                       TEMP = ALPHA*X(JX)
00220                       DO 50 I = 1,M
00221                           Y(I) = Y(I) + TEMP*A(I,J)
00222    50                 CONTINUE
00223                   END IF
00224                   JX = JX + INCX
00225    60         CONTINUE
00226           ELSE
00227               DO 80 J = 1,N
00228                   IF (X(JX).NE.ZERO) THEN
00229                       TEMP = ALPHA*X(JX)
00230                       IY = KY
00231                       DO 70 I = 1,M
00232                           Y(IY) = Y(IY) + TEMP*A(I,J)
00233                           IY = IY + INCY
00234    70                 CONTINUE
00235                   END IF
00236                   JX = JX + INCX
00237    80         CONTINUE
00238           END IF
00239       ELSE
00240 *
00241 *        Form  y := alpha*A'*x + y  or  y := alpha*conjg( A' )*x + y.
00242 *
00243           JY = KY
00244           IF (INCX.EQ.1) THEN
00245               DO 110 J = 1,N
00246                   TEMP = ZERO
00247                   IF (NOCONJ) THEN
00248                       DO 90 I = 1,M
00249                           TEMP = TEMP + A(I,J)*X(I)
00250    90                 CONTINUE
00251                   ELSE
00252                       DO 100 I = 1,M
00253                           TEMP = TEMP + DCONJG(A(I,J))*X(I)
00254   100                 CONTINUE
00255                   END IF
00256                   Y(JY) = Y(JY) + ALPHA*TEMP
00257                   JY = JY + INCY
00258   110         CONTINUE
00259           ELSE
00260               DO 140 J = 1,N
00261                   TEMP = ZERO
00262                   IX = KX
00263                   IF (NOCONJ) THEN
00264                       DO 120 I = 1,M
00265                           TEMP = TEMP + A(I,J)*X(IX)
00266                           IX = IX + INCX
00267   120                 CONTINUE
00268                   ELSE
00269                       DO 130 I = 1,M
00270                           TEMP = TEMP + DCONJG(A(I,J))*X(IX)
00271                           IX = IX + INCX
00272   130                 CONTINUE
00273                   END IF
00274                   Y(JY) = Y(JY) + ALPHA*TEMP
00275                   JY = JY + INCY
00276   140         CONTINUE
00277           END IF
00278       END IF
00279 *
00280       RETURN
00281 *
00282 *     End of ZGEMV .
00283 *
00284       END