LAPACK 3.3.1
Linear Algebra PACKage

dlarnv.f

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00001       SUBROUTINE DLARNV( IDIST, ISEED, N, X )
00002 *
00003 *  -- LAPACK auxiliary routine (version 3.2) --
00004 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00005 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00006 *     November 2006
00007 *
00008 *     .. Scalar Arguments ..
00009       INTEGER            IDIST, N
00010 *     ..
00011 *     .. Array Arguments ..
00012       INTEGER            ISEED( 4 )
00013       DOUBLE PRECISION   X( * )
00014 *     ..
00015 *
00016 *  Purpose
00017 *  =======
00018 *
00019 *  DLARNV returns a vector of n random real numbers from a uniform or
00020 *  normal distribution.
00021 *
00022 *  Arguments
00023 *  =========
00024 *
00025 *  IDIST   (input) INTEGER
00026 *          Specifies the distribution of the random numbers:
00027 *          = 1:  uniform (0,1)
00028 *          = 2:  uniform (-1,1)
00029 *          = 3:  normal (0,1)
00030 *
00031 *  ISEED   (input/output) INTEGER array, dimension (4)
00032 *          On entry, the seed of the random number generator; the array
00033 *          elements must be between 0 and 4095, and ISEED(4) must be
00034 *          odd.
00035 *          On exit, the seed is updated.
00036 *
00037 *  N       (input) INTEGER
00038 *          The number of random numbers to be generated.
00039 *
00040 *  X       (output) DOUBLE PRECISION array, dimension (N)
00041 *          The generated random numbers.
00042 *
00043 *  Further Details
00044 *  ===============
00045 *
00046 *  This routine calls the auxiliary routine DLARUV to generate random
00047 *  real numbers from a uniform (0,1) distribution, in batches of up to
00048 *  128 using vectorisable code. The Box-Muller method is used to
00049 *  transform numbers from a uniform to a normal distribution.
00050 *
00051 *  =====================================================================
00052 *
00053 *     .. Parameters ..
00054       DOUBLE PRECISION   ONE, TWO
00055       PARAMETER          ( ONE = 1.0D+0, TWO = 2.0D+0 )
00056       INTEGER            LV
00057       PARAMETER          ( LV = 128 )
00058       DOUBLE PRECISION   TWOPI
00059       PARAMETER          ( TWOPI = 6.2831853071795864769252867663D+0 )
00060 *     ..
00061 *     .. Local Scalars ..
00062       INTEGER            I, IL, IL2, IV
00063 *     ..
00064 *     .. Local Arrays ..
00065       DOUBLE PRECISION   U( LV )
00066 *     ..
00067 *     .. Intrinsic Functions ..
00068       INTRINSIC          COS, LOG, MIN, SQRT
00069 *     ..
00070 *     .. External Subroutines ..
00071       EXTERNAL           DLARUV
00072 *     ..
00073 *     .. Executable Statements ..
00074 *
00075       DO 40 IV = 1, N, LV / 2
00076          IL = MIN( LV / 2, N-IV+1 )
00077          IF( IDIST.EQ.3 ) THEN
00078             IL2 = 2*IL
00079          ELSE
00080             IL2 = IL
00081          END IF
00082 *
00083 *        Call DLARUV to generate IL2 numbers from a uniform (0,1)
00084 *        distribution (IL2 <= LV)
00085 *
00086          CALL DLARUV( ISEED, IL2, U )
00087 *
00088          IF( IDIST.EQ.1 ) THEN
00089 *
00090 *           Copy generated numbers
00091 *
00092             DO 10 I = 1, IL
00093                X( IV+I-1 ) = U( I )
00094    10       CONTINUE
00095          ELSE IF( IDIST.EQ.2 ) THEN
00096 *
00097 *           Convert generated numbers to uniform (-1,1) distribution
00098 *
00099             DO 20 I = 1, IL
00100                X( IV+I-1 ) = TWO*U( I ) - ONE
00101    20       CONTINUE
00102          ELSE IF( IDIST.EQ.3 ) THEN
00103 *
00104 *           Convert generated numbers to normal (0,1) distribution
00105 *
00106             DO 30 I = 1, IL
00107                X( IV+I-1 ) = SQRT( -TWO*LOG( U( 2*I-1 ) ) )*
00108      $                       COS( TWOPI*U( 2*I ) )
00109    30       CONTINUE
00110          END IF
00111    40 CONTINUE
00112       RETURN
00113 *
00114 *     End of DLARNV
00115 *
00116       END
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