LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ slamch()

real function slamch ( character  CMACH)

SLAMCH

Purpose:
 SLAMCH determines single precision machine parameters.
Parameters
[in]CMACH
          CMACH is CHARACTER*1
          Specifies the value to be returned by SLAMCH:
          = 'E' or 'e',   SLAMCH := eps
          = 'S' or 's ,   SLAMCH := sfmin
          = 'B' or 'b',   SLAMCH := base
          = 'P' or 'p',   SLAMCH := eps*base
          = 'N' or 'n',   SLAMCH := t
          = 'R' or 'r',   SLAMCH := rnd
          = 'M' or 'm',   SLAMCH := emin
          = 'U' or 'u',   SLAMCH := rmin
          = 'L' or 'l',   SLAMCH := emax
          = 'O' or 'o',   SLAMCH := rmax
          where
          eps   = relative machine precision
          sfmin = safe minimum, such that 1/sfmin does not overflow
          base  = base of the machine
          prec  = eps*base
          t     = number of (base) digits in the mantissa
          rnd   = 1.0 when rounding occurs in addition, 0.0 otherwise
          emin  = minimum exponent before (gradual) underflow
          rmin  = underflow threshold - base**(emin-1)
          emax  = largest exponent before overflow
          rmax  = overflow threshold  - (base**emax)*(1-eps)
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 67 of file slamch.f.

68 *
69 * -- LAPACK auxiliary routine --
70 * -- LAPACK is a software package provided by Univ. of Tennessee, --
71 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
72 *
73 * .. Scalar Arguments ..
74  CHARACTER CMACH
75 * ..
76 *
77 * =====================================================================
78 *
79 * .. Parameters ..
80  REAL ONE, ZERO
81  parameter( one = 1.0e+0, zero = 0.0e+0 )
82 * ..
83 * .. Local Scalars ..
84  REAL RND, EPS, SFMIN, SMALL, RMACH
85 * ..
86 * .. External Functions ..
87  LOGICAL LSAME
88  EXTERNAL lsame
89 * ..
90 * .. Intrinsic Functions ..
91  INTRINSIC digits, epsilon, huge, maxexponent,
92  $ minexponent, radix, tiny
93 * ..
94 * .. Executable Statements ..
95 *
96 *
97 * Assume rounding, not chopping. Always.
98 *
99  rnd = one
100 *
101  IF( one.EQ.rnd ) THEN
102  eps = epsilon(zero) * 0.5
103  ELSE
104  eps = epsilon(zero)
105  END IF
106 *
107  IF( lsame( cmach, 'E' ) ) THEN
108  rmach = eps
109  ELSE IF( lsame( cmach, 'S' ) ) THEN
110  sfmin = tiny(zero)
111  small = one / huge(zero)
112  IF( small.GE.sfmin ) THEN
113 *
114 * Use SMALL plus a bit, to avoid the possibility of rounding
115 * causing overflow when computing 1/sfmin.
116 *
117  sfmin = small*( one+eps )
118  END IF
119  rmach = sfmin
120  ELSE IF( lsame( cmach, 'B' ) ) THEN
121  rmach = radix(zero)
122  ELSE IF( lsame( cmach, 'P' ) ) THEN
123  rmach = eps * radix(zero)
124  ELSE IF( lsame( cmach, 'N' ) ) THEN
125  rmach = digits(zero)
126  ELSE IF( lsame( cmach, 'R' ) ) THEN
127  rmach = rnd
128  ELSE IF( lsame( cmach, 'M' ) ) THEN
129  rmach = minexponent(zero)
130  ELSE IF( lsame( cmach, 'U' ) ) THEN
131  rmach = tiny(zero)
132  ELSE IF( lsame( cmach, 'L' ) ) THEN
133  rmach = maxexponent(zero)
134  ELSE IF( lsame( cmach, 'O' ) ) THEN
135  rmach = huge(zero)
136  ELSE
137  rmach = zero
138  END IF
139 *
140  slamch = rmach
141  RETURN
142 *
143 * End of SLAMCH
144 *
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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