1HPL_pdlamch(3)               HPL Library Functions              HPL_pdlamch(3)
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NAME

6       HPL_pdlamch - determines machine-specific arithmetic constants.
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SYNOPSIS

9       #include "hpl.h"
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11       double HPL_pdlamch( MPI_Comm COMM, const HPL_T_MACH CMACH );
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DESCRIPTION

14       HPL_pdlamch  determines   machine-specific  arithmetic  constants  such
15       as the relative machine precision (eps),  the safe minimum(sfmin)  such
16       that  1/sfmin  does  not  overflow, the base of the machine (base), the
17       precision (prec),  the  number  of  (base)   digits  in  the   mantissa
18       (t),   whether  rounding  occurs  in addition (rnd = 1.0 and 0.0 other‐
19       wise),  the  minimum exponent before  (gradual)  underflow (emin),  the
20       underflow   threshold  (rmin)-  base**(emin-1),  the  largest  exponent
21       before   overflow   (emax),   the   overflow   threshold   (rmax)     -
22       (base**emax)*(1-eps).
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ARGUMENTS

25       COMM    (global/local input)    MPI_Comm
26               The MPI communicator identifying the process collection.
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28       CMACH   (global input)          const HPL_T_MACH
29               Specifies the value to be returned by HPL_pdlamch
30                  = HPL_MACH_EPS,   HPL_pdlamch := eps (default)
31                  = HPL_MACH_SFMIN, HPL_pdlamch := sfmin
32                  = HPL_MACH_BASE,  HPL_pdlamch := base
33                  = HPL_MACH_PREC,  HPL_pdlamch := eps*base
34                  = HPL_MACH_MLEN,  HPL_pdlamch := t
35                  = HPL_MACH_RND,   HPL_pdlamch := rnd
36                  = HPL_MACH_EMIN,  HPL_pdlamch := emin
37                  = HPL_MACH_RMIN,  HPL_pdlamch := rmin
38                  = HPL_MACH_EMAX,  HPL_pdlamch := emax
39                  = HPL_MACH_RMAX,  HPL_pdlamch := rmax
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41               where
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43                  eps   = relative machine precision,
44                  sfmin = safe minimum,
45                  base  = base of the machine,
46                  prec  = eps*base,
47                  t     = number of digits in the mantissa,
48                  rnd   = 1.0 if rounding occurs in addition,
49                  emin  = minimum exponent before underflow,
50                  rmin  = underflow threshold,
51                  emax  = largest exponent before overflow,
52                  rmax  = overflow threshold.
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56HPL 2.1                        October 26, 2012                 HPL_pdlamch(3)
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