#!/usr/bin/python
# -*- coding: utf8 -*-
# Uncertain quantities.
# (c) Robert Jordens <jordens@debian.org>
# Made available freely under the Python license
import numpy as np
from enthought.traits.api import HasStrictTraits
from enthought.traits.api import Str, Float, Bool, List, Dict, Enum
class Uncertain(HasStrictTraits):
"""
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.
The usage of traits can easily be dumped.
"""
value = Float
error = Float(0.)
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 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.))**2+
(other.error*np.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*np.log(other)*other**self.value)
def exp(self):
return np.e**self
def log(self):
return Uncertain(np.log(self.value), self.error/self.value)
