Annotation of rpl/lapack/lapack/zsyr.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE ZSYR( UPLO, N, ALPHA, X, INCX, A, LDA )
! 2: *
! 3: * -- LAPACK auxiliary routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: CHARACTER UPLO
! 10: INTEGER INCX, LDA, N
! 11: COMPLEX*16 ALPHA
! 12: * ..
! 13: * .. Array Arguments ..
! 14: COMPLEX*16 A( LDA, * ), X( * )
! 15: * ..
! 16: *
! 17: * Purpose
! 18: * =======
! 19: *
! 20: * ZSYR performs the symmetric rank 1 operation
! 21: *
! 22: * A := alpha*x*( x' ) + A,
! 23: *
! 24: * where alpha is a complex scalar, x is an n element vector and A is an
! 25: * n by n symmetric matrix.
! 26: *
! 27: * Arguments
! 28: * ==========
! 29: *
! 30: * UPLO (input) CHARACTER*1
! 31: * On entry, UPLO specifies whether the upper or lower
! 32: * triangular part of the array A is to be referenced as
! 33: * follows:
! 34: *
! 35: * UPLO = 'U' or 'u' Only the upper triangular part of A
! 36: * is to be referenced.
! 37: *
! 38: * UPLO = 'L' or 'l' Only the lower triangular part of A
! 39: * is to be referenced.
! 40: *
! 41: * Unchanged on exit.
! 42: *
! 43: * N (input) INTEGER
! 44: * On entry, N specifies the order of the matrix A.
! 45: * N must be at least zero.
! 46: * Unchanged on exit.
! 47: *
! 48: * ALPHA (input) COMPLEX*16
! 49: * On entry, ALPHA specifies the scalar alpha.
! 50: * Unchanged on exit.
! 51: *
! 52: * X (input) COMPLEX*16 array, dimension at least
! 53: * ( 1 + ( N - 1 )*abs( INCX ) ).
! 54: * Before entry, the incremented array X must contain the N-
! 55: * element vector x.
! 56: * Unchanged on exit.
! 57: *
! 58: * INCX (input) INTEGER
! 59: * On entry, INCX specifies the increment for the elements of
! 60: * X. INCX must not be zero.
! 61: * Unchanged on exit.
! 62: *
! 63: * A (input/output) COMPLEX*16 array, dimension ( LDA, N )
! 64: * Before entry, with UPLO = 'U' or 'u', the leading n by n
! 65: * upper triangular part of the array A must contain the upper
! 66: * triangular part of the symmetric matrix and the strictly
! 67: * lower triangular part of A is not referenced. On exit, the
! 68: * upper triangular part of the array A is overwritten by the
! 69: * upper triangular part of the updated matrix.
! 70: * Before entry, with UPLO = 'L' or 'l', the leading n by n
! 71: * lower triangular part of the array A must contain the lower
! 72: * triangular part of the symmetric matrix and the strictly
! 73: * upper triangular part of A is not referenced. On exit, the
! 74: * lower triangular part of the array A is overwritten by the
! 75: * lower triangular part of the updated matrix.
! 76: *
! 77: * LDA (input) INTEGER
! 78: * On entry, LDA specifies the first dimension of A as declared
! 79: * in the calling (sub) program. LDA must be at least
! 80: * max( 1, N ).
! 81: * Unchanged on exit.
! 82: *
! 83: * =====================================================================
! 84: *
! 85: * .. Parameters ..
! 86: COMPLEX*16 ZERO
! 87: PARAMETER ( ZERO = ( 0.0D+0, 0.0D+0 ) )
! 88: * ..
! 89: * .. Local Scalars ..
! 90: INTEGER I, INFO, IX, J, JX, KX
! 91: COMPLEX*16 TEMP
! 92: * ..
! 93: * .. External Functions ..
! 94: LOGICAL LSAME
! 95: EXTERNAL LSAME
! 96: * ..
! 97: * .. External Subroutines ..
! 98: EXTERNAL XERBLA
! 99: * ..
! 100: * .. Intrinsic Functions ..
! 101: INTRINSIC MAX
! 102: * ..
! 103: * .. Executable Statements ..
! 104: *
! 105: * Test the input parameters.
! 106: *
! 107: INFO = 0
! 108: IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
! 109: INFO = 1
! 110: ELSE IF( N.LT.0 ) THEN
! 111: INFO = 2
! 112: ELSE IF( INCX.EQ.0 ) THEN
! 113: INFO = 5
! 114: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
! 115: INFO = 7
! 116: END IF
! 117: IF( INFO.NE.0 ) THEN
! 118: CALL XERBLA( 'ZSYR ', INFO )
! 119: RETURN
! 120: END IF
! 121: *
! 122: * Quick return if possible.
! 123: *
! 124: IF( ( N.EQ.0 ) .OR. ( ALPHA.EQ.ZERO ) )
! 125: $ RETURN
! 126: *
! 127: * Set the start point in X if the increment is not unity.
! 128: *
! 129: IF( INCX.LE.0 ) THEN
! 130: KX = 1 - ( N-1 )*INCX
! 131: ELSE IF( INCX.NE.1 ) THEN
! 132: KX = 1
! 133: END IF
! 134: *
! 135: * Start the operations. In this version the elements of A are
! 136: * accessed sequentially with one pass through the triangular part
! 137: * of A.
! 138: *
! 139: IF( LSAME( UPLO, 'U' ) ) THEN
! 140: *
! 141: * Form A when A is stored in upper triangle.
! 142: *
! 143: IF( INCX.EQ.1 ) THEN
! 144: DO 20 J = 1, N
! 145: IF( X( J ).NE.ZERO ) THEN
! 146: TEMP = ALPHA*X( J )
! 147: DO 10 I = 1, J
! 148: A( I, J ) = A( I, J ) + X( I )*TEMP
! 149: 10 CONTINUE
! 150: END IF
! 151: 20 CONTINUE
! 152: ELSE
! 153: JX = KX
! 154: DO 40 J = 1, N
! 155: IF( X( JX ).NE.ZERO ) THEN
! 156: TEMP = ALPHA*X( JX )
! 157: IX = KX
! 158: DO 30 I = 1, J
! 159: A( I, J ) = A( I, J ) + X( IX )*TEMP
! 160: IX = IX + INCX
! 161: 30 CONTINUE
! 162: END IF
! 163: JX = JX + INCX
! 164: 40 CONTINUE
! 165: END IF
! 166: ELSE
! 167: *
! 168: * Form A when A is stored in lower triangle.
! 169: *
! 170: IF( INCX.EQ.1 ) THEN
! 171: DO 60 J = 1, N
! 172: IF( X( J ).NE.ZERO ) THEN
! 173: TEMP = ALPHA*X( J )
! 174: DO 50 I = J, N
! 175: A( I, J ) = A( I, J ) + X( I )*TEMP
! 176: 50 CONTINUE
! 177: END IF
! 178: 60 CONTINUE
! 179: ELSE
! 180: JX = KX
! 181: DO 80 J = 1, N
! 182: IF( X( JX ).NE.ZERO ) THEN
! 183: TEMP = ALPHA*X( JX )
! 184: IX = JX
! 185: DO 70 I = J, N
! 186: A( I, J ) = A( I, J ) + X( IX )*TEMP
! 187: IX = IX + INCX
! 188: 70 CONTINUE
! 189: END IF
! 190: JX = JX + INCX
! 191: 80 CONTINUE
! 192: END IF
! 193: END IF
! 194: *
! 195: RETURN
! 196: *
! 197: * End of ZSYR
! 198: *
! 199: END
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