SRC\pdlabad.f
#lines: 75   size: 2 Kb   creation: 18/01/2006 23:36:04   last modification: 08/05/2008 18:37:53   attribute: ARCH    Find   Reload   
1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
25:
26:
27:
28:
29:
30:
31:
32:
33:
34:
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
45:
46:
47:
48:
49:
50:
51:
52:
53:
54:
55:
56:
57:
58:
59:
60:
61:
62:
63:
64:
65:
66:
67:
68:
69:
70:
71:
72:
73:
74:
75:
 
      SUBROUTINE PDLABAD( ICTXT, SMALL, LARGE )
*
*  -- ScaLAPACK auxiliary routine (version 1.7) --
*     University of Tennessee, Knoxville, Oak Ridge National Laboratory,
*     and University of California, Berkeley.
*     May 1, 1997
*
*     .. Scalar Arguments ..
      INTEGER            ICTXT
      DOUBLE PRECISION   LARGE, SMALL
*     ..
*
*  Purpose
*  =======
*
*  PDLABAD takes as input the values computed by PDLAMCH for underflow
*  and overflow, and returns the square root of each of these values if
*  the log of LARGE is sufficiently large.  This subroutine is intended
*  to identify machines with a large exponent range, such as the Crays,
*  and redefine the underflow and overflow limits to be the square roots
*  of the values computed by PDLAMCH.  This subroutine is needed because
*  PDLAMCH does not compensate for poor arithmetic in the upper half of
*  the exponent range, as is found on a Cray.
*
*  In addition, this routine performs a global minimization and maximi-
*  zation on these values, to support heterogeneous computing networks.
*
*  Arguments
*  =========
*
*  ICTXT   (global input) INTEGER
*          The BLACS context handle in which the computation takes
*          place.
*
*  SMALL   (local input/local output) DOUBLE PRECISION
*          On entry, the underflow threshold as computed by PDLAMCH.
*          On exit, if LOG10(LARGE) is sufficiently large, the square
*          root of SMALL, otherwise unchanged.
*
*  LARGE   (local input/local output) DOUBLE PRECISION
*          On entry, the overflow threshold as computed by PDLAMCH.
*          On exit, if LOG10(LARGE) is sufficiently large, the square
*          root of LARGE, otherwise unchanged.
*
*  =====================================================================
*
*     .. Local Scalars ..
      INTEGER            IDUMM
*     ..
*     .. External Subroutines ..
      EXTERNAL           DGAMN2D, DGAMX2D
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          LOG10, SQRT
*     ..
*     .. Executable Statements ..
*
*     If it looks like we're on a Cray, take the square root of
*     SMALL and LARGE to avoid overflow and underflow problems.
*
      IF( LOG10( LARGE ).GT.2000.D0 ) THEN
         SMALL = SQRT( SMALL )
         LARGE = SQRT( LARGE )
      END IF
*
      CALL DGAMX2D( ICTXT, 'All', ' ', 1, 1, SMALL, 1, IDUMM,
     $              IDUMM, -1, -1, IDUMM )
      CALL DGAMN2D( ICTXT, 'All', ' ', 1, 1, LARGE, 1, IDUMM,
     $              IDUMM, -1, -1, IDUMM )
*
      RETURN
*
*     End of PDLABAD
*
      END