Geometric Brownian Motion Stochastic Process

GeometricBrownianMotion.py

import math
import numpy
import random
import decimal
import scipy.linalg
import numpy.random as nrand
import matplotlib.pyplot as plt

"""
Note that this Gist uses the Model Parameters class found here  - https://gist.github.com/StuartGordonReid/f01f479c783dd40cc21e
"""

def geometric_brownian_motion_log_returns(param):
    """
    This method constructs a sequence of log returns which, when exponentiated, produce a random Geometric Brownian
    Motion (GBM). GBM is the stochastic process underlying the Black Scholes options pricing formula.
    :param param: model parameters object
    :return: returns the log returns of a geometric brownian motion process
    """
    assert isinstance(param, ModelParameters)
    wiener_process = numpy.array(brownian_motion_log_returns(param))
    sigma_pow_mu_delta = (param.gbm_mu - 0.5 * math.pow(param.all_sigma, 2.0)) * param.all_delta
    return wiener_process + sigma_pow_mu_delta


def geometric_brownian_motion_levels(param):
    """
    Returns a sequence of price levels for an asset which evolves according to a geometric brownian motion
    :param param: model parameters object
    :return: the price levels for the asset
    """
    return convert_to_prices(param, geometric_brownian_motion_log_returns(param))