Current File : //lib/python3/dist-packages/sympy/codegen/scipy_nodes.py
from sympy.core.function import Add, ArgumentIndexError, Function
from sympy.core.singleton import S
from sympy.functions.elementary.trigonometric import cos, sin
def _cosm1(x, *, evaluate=True):
return Add(cos(x, evaluate=evaluate), -S.One, evaluate=evaluate)
class cosm1(Function):
""" Minus one plus cosine of x, i.e. cos(x) - 1. For use when x is close to zero.
Helper class for use with e.g. scipy.special.cosm1
See: https://docs.scipy.org/doc/scipy/reference/generated/scipy.special.cosm1.html
"""
nargs = 1
def fdiff(self, argindex=1):
"""
Returns the first derivative of this function.
"""
if argindex == 1:
return -sin(*self.args)
else:
raise ArgumentIndexError(self, argindex)
def _eval_rewrite_as_cos(self, x, **kwargs):
return _cosm1(x)
def _eval_evalf(self, *args, **kwargs):
return self.rewrite(cos).evalf(*args, **kwargs)
def _eval_simplify(self, x, **kwargs):
candidate = _cosm1(x.simplify(**kwargs))
if candidate != _cosm1(x, evaluate=False):
return candidate
else:
return cosm1(x)
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