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51 lines
1.4 KiB
Python
51 lines
1.4 KiB
Python
import numpy as np
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from Link import Link
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class RubberBand:
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# class attributes
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def __init__(self, N, a=1., kBT=1., biased=False, force=0.):
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"""
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RubberBand is a class that can simulate a rubber band with N
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incompressible links of length a.
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Parameters
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----------
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N : int
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The number of links.
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a : float, optional
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The fixed length of the links. The default is 1..
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kBT : float, optional
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Temperature of the system (arb. units). The default is 1..
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force : float, optional
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Force applied to the RubberBand.
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The default is 0, which is an unbiased RubberBand.
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"""
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self.N = N
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self.a = a
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self.kBT = kBT
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self.links = self.__sample_links(force=force)
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def w(self, f, l):
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beta = (self.kBT)**(-1)
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return np.exp(beta*f*l)
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@property
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def length(self):
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return self.a * np.sum([l.direction for l in self.links])
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def __sample_links(self, force):
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"""
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Sample N Link objects with a random direction.
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"""
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samples = np.random.random_sample((self.N,))
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directions = np.ones(samples.shape)
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p_negative = 1 - 0.5*(1 + np.tanh(force*self.a/self.kBT))
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directions[samples < p_negative] = -1.
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directions = directions.astype(int)
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return [Link(d) for d in directions] |