LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ dlamch()

double precision function dlamch ( character  CMACH)

DLAMCH

Purpose:
 DLAMCH determines double precision machine parameters.
Parameters
[in]CMACH
          CMACH is CHARACTER*1
          Specifies the value to be returned by DLAMCH:
          = 'E' or 'e',   DLAMCH := eps
          = 'S' or 's ,   DLAMCH := sfmin
          = 'B' or 'b',   DLAMCH := base
          = 'P' or 'p',   DLAMCH := eps*base
          = 'N' or 'n',   DLAMCH := t
          = 'R' or 'r',   DLAMCH := rnd
          = 'M' or 'm',   DLAMCH := emin
          = 'U' or 'u',   DLAMCH := rmin
          = 'L' or 'l',   DLAMCH := emax
          = 'O' or 'o',   DLAMCH := 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 68 of file dlamch.f.

69 *
70 * -- LAPACK auxiliary routine --
71 * -- LAPACK is a software package provided by Univ. of Tennessee, --
72 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
73 *
74 * .. Scalar Arguments ..
75  CHARACTER CMACH
76 * ..
77 *
78 * =====================================================================
79 *
80 * .. Parameters ..
81  DOUBLE PRECISION ONE, ZERO
82  parameter( one = 1.0d+0, zero = 0.0d+0 )
83 * ..
84 * .. Local Scalars ..
85  DOUBLE PRECISION RND, EPS, SFMIN, SMALL, RMACH
86 * ..
87 * .. External Functions ..
88  LOGICAL LSAME
89  EXTERNAL lsame
90 * ..
91 * .. Intrinsic Functions ..
92  INTRINSIC digits, epsilon, huge, maxexponent,
93  $ minexponent, radix, tiny
94 * ..
95 * .. Executable Statements ..
96 *
97 *
98 * Assume rounding, not chopping. Always.
99 *
100  rnd = one
101 *
102  IF( one.EQ.rnd ) THEN
103  eps = epsilon(zero) * 0.5
104  ELSE
105  eps = epsilon(zero)
106  END IF
107 *
108  IF( lsame( cmach, 'E' ) ) THEN
109  rmach = eps
110  ELSE IF( lsame( cmach, 'S' ) ) THEN
111  sfmin = tiny(zero)
112  small = one / huge(zero)
113  IF( small.GE.sfmin ) THEN
114 *
115 * Use SMALL plus a bit, to avoid the possibility of rounding
116 * causing overflow when computing 1/sfmin.
117 *
118  sfmin = small*( one+eps )
119  END IF
120  rmach = sfmin
121  ELSE IF( lsame( cmach, 'B' ) ) THEN
122  rmach = radix(zero)
123  ELSE IF( lsame( cmach, 'P' ) ) THEN
124  rmach = eps * radix(zero)
125  ELSE IF( lsame( cmach, 'N' ) ) THEN
126  rmach = digits(zero)
127  ELSE IF( lsame( cmach, 'R' ) ) THEN
128  rmach = rnd
129  ELSE IF( lsame( cmach, 'M' ) ) THEN
130  rmach = minexponent(zero)
131  ELSE IF( lsame( cmach, 'U' ) ) THEN
132  rmach = tiny(zero)
133  ELSE IF( lsame( cmach, 'L' ) ) THEN
134  rmach = maxexponent(zero)
135  ELSE IF( lsame( cmach, 'O' ) ) THEN
136  rmach = huge(zero)
137  ELSE
138  rmach = zero
139  END IF
140 *
141  dlamch = rmach
142  RETURN
143 *
144 * End of DLAMCH
145 *
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
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