LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ 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*
dlamch
double precision function dlamch(cmach)
DLAMCH
Definition dlamch.f:69
lsame
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
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