Annotation of rpl/lapack/blas/dspr.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DSPR(UPLO,N,ALPHA,X,INCX,AP)
! 2: * .. Scalar Arguments ..
! 3: DOUBLE PRECISION ALPHA
! 4: INTEGER INCX,N
! 5: CHARACTER UPLO
! 6: * ..
! 7: * .. Array Arguments ..
! 8: DOUBLE PRECISION AP(*),X(*)
! 9: * ..
! 10: *
! 11: * Purpose
! 12: * =======
! 13: *
! 14: * DSPR performs the symmetric rank 1 operation
! 15: *
! 16: * A := alpha*x*x' + A,
! 17: *
! 18: * where alpha is a real scalar, x is an n element vector and A is an
! 19: * n by n symmetric matrix, supplied in packed form.
! 20: *
! 21: * Arguments
! 22: * ==========
! 23: *
! 24: * UPLO - CHARACTER*1.
! 25: * On entry, UPLO specifies whether the upper or lower
! 26: * triangular part of the matrix A is supplied in the packed
! 27: * array AP as follows:
! 28: *
! 29: * UPLO = 'U' or 'u' The upper triangular part of A is
! 30: * supplied in AP.
! 31: *
! 32: * UPLO = 'L' or 'l' The lower triangular part of A is
! 33: * supplied in AP.
! 34: *
! 35: * Unchanged on exit.
! 36: *
! 37: * N - INTEGER.
! 38: * On entry, N specifies the order of the matrix A.
! 39: * N must be at least zero.
! 40: * Unchanged on exit.
! 41: *
! 42: * ALPHA - DOUBLE PRECISION.
! 43: * On entry, ALPHA specifies the scalar alpha.
! 44: * Unchanged on exit.
! 45: *
! 46: * X - DOUBLE PRECISION array of dimension at least
! 47: * ( 1 + ( n - 1 )*abs( INCX ) ).
! 48: * Before entry, the incremented array X must contain the n
! 49: * element vector x.
! 50: * Unchanged on exit.
! 51: *
! 52: * INCX - INTEGER.
! 53: * On entry, INCX specifies the increment for the elements of
! 54: * X. INCX must not be zero.
! 55: * Unchanged on exit.
! 56: *
! 57: * AP - DOUBLE PRECISION array of DIMENSION at least
! 58: * ( ( n*( n + 1 ) )/2 ).
! 59: * Before entry with UPLO = 'U' or 'u', the array AP must
! 60: * contain the upper triangular part of the symmetric matrix
! 61: * packed sequentially, column by column, so that AP( 1 )
! 62: * contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 )
! 63: * and a( 2, 2 ) respectively, and so on. On exit, the array
! 64: * AP is overwritten by the upper triangular part of the
! 65: * updated matrix.
! 66: * Before entry with UPLO = 'L' or 'l', the array AP must
! 67: * contain the lower triangular part of the symmetric matrix
! 68: * packed sequentially, column by column, so that AP( 1 )
! 69: * contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 )
! 70: * and a( 3, 1 ) respectively, and so on. On exit, the array
! 71: * AP is overwritten by the lower triangular part of the
! 72: * updated matrix.
! 73: *
! 74: * Further Details
! 75: * ===============
! 76: *
! 77: * Level 2 Blas routine.
! 78: *
! 79: * -- Written on 22-October-1986.
! 80: * Jack Dongarra, Argonne National Lab.
! 81: * Jeremy Du Croz, Nag Central Office.
! 82: * Sven Hammarling, Nag Central Office.
! 83: * Richard Hanson, Sandia National Labs.
! 84: *
! 85: * =====================================================================
! 86: *
! 87: * .. Parameters ..
! 88: DOUBLE PRECISION ZERO
! 89: PARAMETER (ZERO=0.0D+0)
! 90: * ..
! 91: * .. Local Scalars ..
! 92: DOUBLE PRECISION TEMP
! 93: INTEGER I,INFO,IX,J,JX,K,KK,KX
! 94: * ..
! 95: * .. External Functions ..
! 96: LOGICAL LSAME
! 97: EXTERNAL LSAME
! 98: * ..
! 99: * .. External Subroutines ..
! 100: EXTERNAL XERBLA
! 101: * ..
! 102: *
! 103: * Test the input parameters.
! 104: *
! 105: INFO = 0
! 106: IF (.NOT.LSAME(UPLO,'U') .AND. .NOT.LSAME(UPLO,'L')) THEN
! 107: INFO = 1
! 108: ELSE IF (N.LT.0) THEN
! 109: INFO = 2
! 110: ELSE IF (INCX.EQ.0) THEN
! 111: INFO = 5
! 112: END IF
! 113: IF (INFO.NE.0) THEN
! 114: CALL XERBLA('DSPR ',INFO)
! 115: RETURN
! 116: END IF
! 117: *
! 118: * Quick return if possible.
! 119: *
! 120: IF ((N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
! 121: *
! 122: * Set the start point in X if the increment is not unity.
! 123: *
! 124: IF (INCX.LE.0) THEN
! 125: KX = 1 - (N-1)*INCX
! 126: ELSE IF (INCX.NE.1) THEN
! 127: KX = 1
! 128: END IF
! 129: *
! 130: * Start the operations. In this version the elements of the array AP
! 131: * are accessed sequentially with one pass through AP.
! 132: *
! 133: KK = 1
! 134: IF (LSAME(UPLO,'U')) THEN
! 135: *
! 136: * Form A when upper triangle is stored in AP.
! 137: *
! 138: IF (INCX.EQ.1) THEN
! 139: DO 20 J = 1,N
! 140: IF (X(J).NE.ZERO) THEN
! 141: TEMP = ALPHA*X(J)
! 142: K = KK
! 143: DO 10 I = 1,J
! 144: AP(K) = AP(K) + X(I)*TEMP
! 145: K = K + 1
! 146: 10 CONTINUE
! 147: END IF
! 148: KK = KK + J
! 149: 20 CONTINUE
! 150: ELSE
! 151: JX = KX
! 152: DO 40 J = 1,N
! 153: IF (X(JX).NE.ZERO) THEN
! 154: TEMP = ALPHA*X(JX)
! 155: IX = KX
! 156: DO 30 K = KK,KK + J - 1
! 157: AP(K) = AP(K) + X(IX)*TEMP
! 158: IX = IX + INCX
! 159: 30 CONTINUE
! 160: END IF
! 161: JX = JX + INCX
! 162: KK = KK + J
! 163: 40 CONTINUE
! 164: END IF
! 165: ELSE
! 166: *
! 167: * Form A when lower triangle is stored in AP.
! 168: *
! 169: IF (INCX.EQ.1) THEN
! 170: DO 60 J = 1,N
! 171: IF (X(J).NE.ZERO) THEN
! 172: TEMP = ALPHA*X(J)
! 173: K = KK
! 174: DO 50 I = J,N
! 175: AP(K) = AP(K) + X(I)*TEMP
! 176: K = K + 1
! 177: 50 CONTINUE
! 178: END IF
! 179: KK = KK + N - J + 1
! 180: 60 CONTINUE
! 181: ELSE
! 182: JX = KX
! 183: DO 80 J = 1,N
! 184: IF (X(JX).NE.ZERO) THEN
! 185: TEMP = ALPHA*X(JX)
! 186: IX = JX
! 187: DO 70 K = KK,KK + N - J
! 188: AP(K) = AP(K) + X(IX)*TEMP
! 189: IX = IX + INCX
! 190: 70 CONTINUE
! 191: END IF
! 192: JX = JX + INCX
! 193: KK = KK + N - J + 1
! 194: 80 CONTINUE
! 195: END IF
! 196: END IF
! 197: *
! 198: RETURN
! 199: *
! 200: * End of DSPR .
! 201: *
! 202: END
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