2011/06/19

calculate cosine with python numpy

purpose


Calculate "cosine" determined by pair of vectors using python and its package named numpy. Firstly I show you the definition of cosine in linear space, and Secondly I share sample python code for calculating cosine.

definition of cosine in linear space






python code for calculating cosine


import numpy

def get_cosine(v1, v2):
""" calculate cosine and returns cosine """
n1 = get_norm_of_vector(v1)
n2 = get_norm_of_vector(v2)
ip = get_inner_product(v1, v2)
return ip / (n1 * n2)

def get_inner_product(v1, v2):
""" calculate inner product """
return numpy.dot(v1, v2)

def get_norm_of_vector(v):
""" calculate norm of vector """
return numpy.linalg.norm(v)

def get_radian_from_cosine(cos):
return numpy.arccos(cos)

def get_degrees_from_radian(cos):
return numpy.degrees(cos)

def main():
v1 = numpy.array([1, 0])
v2 = numpy.array([1, numpy.sqrt(3)])
cosine = get_cosine(v1, v2)
radian = get_radian_from_cosine(cosine)
print get_degrees_from_radian(radian)

if __name__ == "__main__":
main()

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