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double precision function epslon (x)
double precision x
c
c estimate unit roundoff in quantities of size x.
c
double precision a,b,c,eps
c
c this program should function properly on all systems
c satisfying the following two assumptions,
c 1. the base used in representing floating point
c numbers is not a power of three.
c 2. the quantity a in statement 10 is represented to
c the accuracy used in floating point variables
c that are stored in memory.
c the statement number 10 and the go to 10 are intended to
c force optimizing compilers to generate code satisfying
c assumption 2.
c under these assumptions, it should be true that,
c a is not exactly equal to four-thirds,
c b has a zero for its last bit or digit,
c c is not exactly equal to one,
c eps measures the separation of 1.0 from
c the next larger floating point number.
c the developers of eispack would appreciate being informed
c about any systems where these assumptions do not hold.
c
c this version dated 4/6/83.
c
a = 4.0d0/3.0d0
10 b = a - 1.0d0
c = b + b + b
eps = dabs(c-1.0d0)
if (eps .eq. 0.0d0) go to 10
epslon = eps*dabs(x)
return
end
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