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)```

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,
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
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:48
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