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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
# ELOGD -- Extended range log function. Logarithmic scaling function for
# negative or partially negative data. The function is piecewise, continuous,
# monotonic, reasonably smooth, and most importantly, is defined for all x.
#
# 10.0 < X y = log(x)
# -10.0 <= X <= 10.0 y = x / 10.0
# X < -10.0 y = -log(-x)
#
# Axes scaled with this function should have ticks labelled, e.g., 10**3,
# 10**2, 10**1, 0, -10**1, -10**2, -10**3. The corresponding ticks for
# the normal log function would have values like 10**-2 rather than -10**2,
# hence it is not difficult to distinguish between the two functions.
double procedure elogd (x)
double x
begin
if (x > 10.0D0)
return (log10 (x))
else if (x >= -10.0D0)
return (x / 10.0D0)
else
return (-log10 (-x))
end
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