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  r76861 | mark.dickinson | 2009-12-16 20:13:40 +0000 (Wed, 16 Dec 2009) | 3 lines

  Issue #3366: Add expm1 function to math module.  Thanks Eric Smith for
  testing on Windows.
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Mark Dickinson 2009-12-16 20:23:42 +00:00
parent ef1992b9fb
commit 664b511c0a
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14
Doc/library/math.rst
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@ -148,6 +148,20 @@ Power and logarithmic functions
Return ``e**x``.
.. function:: expm1(x)
Return ``e**x - 1``. For small floats *x*, the subtraction in
``exp(x) - 1`` can result in a significant loss of precision; the
:func:`expm1` function provides a way to compute this quantity to
full precision::
>>> from math import exp, expm1
>>> exp(1e-5) - 1 # gives result accurate to 11 places
1.0000050000069649e-05
>>> expm1(1e-5) # result accurate to full precision
1.0000050000166668e-05
.. function:: log(x[, base])
With one argument, return the natural logarithm of *x* (to base *e*).