Source code for tkp.utility.uncertain
#
# LOFAR Transients Key Project
#
# Uncertain quantities.
# Based on:
# (c) Robert Jordens <jordens@debian.org>
# Made available freely under the Python license
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/535164
import math
[docs]class Uncertain(object):
"""Represents a numeric value with a known small uncertainty (error,
standard deviation...).
Numeric operators are overloaded to work with other Uncertain or
numeric objects. The uncertainty (error) must be small. Otherwise
the linearization employed here becomes wrong.
"""
def __init__(self, value=0., error=0., *a, **t):
self.value = value
self.error = abs(error)
super(Uncertain, self).__init__(*a, **t)
def __str__(self):
return "%g+-%g" % (self.value, self.error)
def __repr__(self):
return "Uncertain(%s, %s)" % (self.value, self.error)
def __float__(self):
return float(self.value)
def assign(self, other):
if isinstance(other, Uncertain):
self.value = other.value
self.error = other.error
else:
self.value = other
self.error = 0.
def __abs__(self):
return Uncertain(abs(self.value), self.error)
def __add__(self, other):
if isinstance(other, Uncertain):
v = self.value + other.value
e = (self.error**2 + other.error**2)**.5
return Uncertain(v, e)
else:
return Uncertain(self.value + other, self.error)
def __radd__(self, other):
return self + other # __add__
def __sub__(self, other):
return self + (-other) # other.__neg__ and __add__
def __rsub__(self, other):
return -self + other # __neg__ and __add__
def __mul__(self, other):
if isinstance(other, Uncertain):
v = self.value * other.value
e = ((self.error * other.value)**2 +
(other.error * self.value)**2)**.5
return Uncertain(v, e)
else:
return Uncertain(self.value * other, self.error * other)
def __rmul__(self, other):
return self * other # __mul__
def __neg__(self):
return self * -1 # __mul__
def __pos__(self):
return self
def __div__(self, other):
return self * (1. / other) # other.__div__ and __mul__
def __rdiv__(self, other):
return (self / other)**-1. # __pow__ and __div__
def __pow__(self, other):
if isinstance(other, Uncertain):
v = self.value**other.value
e = ((self.error * other.value *
self.value**(other.value - 1.0))**2 +
(other.error * math.log(self.value) *
self.value**other.value)**2
)**.5
return Uncertain(v, e)
else:
return Uncertain(self.value**other,
self.error * other * self.value**(other - 1))
def __rpow__(self, other):
assert not isinstance(other, Uncertain)
# otherwise other.__pow__ would have been called
return Uncertain(other**self.value,
self.error * math.log(other) * other**self.value)
def __cmp__(self, compare):
try:
return cmp(self.value, compare.value)
except AttributeError:
return cmp(self.value, compare)
def exp(self):
return math.e**self
def log(self):
return Uncertain(math.log(self.value), self.error / self.value)
def max(self):
return self.value + self.error
def min(self):
return self.value - self.error