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#!/usr/bin/env python
"""
Bevington & Robinson's model of dual exponential decay
References::
[5] Bevington & Robinson (1992).
Data Reduction and Error Analysis for the Physical Sciences,
Second Edition, McGraw-Hill, Inc., New York.
"""
import numpy as np
from numpy import exp, inf, sqrt
def dual_exponential(t, a):
"""
Computes dual exponential decay.
y = a1 + a2 exp(-t/a3) + a4 exp(-t/a5)
"""
a1, a2, a3, a4, a5 = a
t = np.asarray(t)
return a1 + a2 * exp(-t / a4) + a3 * exp(-t / a5)
# data from Chapter 8 of [5].
data = np.array(
[
[15, 775],
[30, 479],
[45, 380],
[60, 302],
[75, 185],
[90, 157],
[105, 137],
[120, 119],
[135, 110],
[150, 89],
[165, 74],
[180, 61],
[195, 66],
[210, 68],
[225, 48],
[240, 54],
[255, 51],
[270, 46],
[285, 55],
[300, 29],
[315, 28],
[330, 37],
[345, 49],
[360, 26],
[375, 35],
[390, 29],
[405, 31],
[420, 24],
[435, 25],
[450, 35],
[465, 24],
[480, 30],
[495, 26],
[510, 28],
[525, 21],
[540, 18],
[555, 20],
[570, 27],
[585, 17],
[600, 17],
[615, 14],
[630, 17],
[645, 24],
[660, 11],
[675, 22],
[690, 17],
[705, 12],
[720, 10],
[735, 13],
[750, 16],
[765, 9],
[780, 9],
[795, 14],
[810, 21],
[825, 17],
[840, 13],
[855, 12],
[870, 18],
[885, 10],
]
)
x = data[:, 0]
y = data[:, 1]
dy = sqrt(data[:, 1])
Po = [1, 1, 1, 1, 1]
Plo = [-inf, 0, 0, 0, 0]
Phi = [inf, inf, inf, inf, inf]
from .model import Fitness
decay = Fitness(f=dual_exponential, data=(x, y, dy), limits=(Plo, Phi), start=Po)
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