ObjSim/python/objsimpy/distance.py

# -*- coding: utf-8 -*-
"""
Created on 18.06.2014

@author: frank
"""
import numpy as np

def test():
    pass

def cyclic_distance(a, b, base):
    """Calculate distance between two elements a and b of a residue class ring with modulo base
    
    :param a: first element (scalar or numpy array)
    :param b: second element (scalar or numpy array)
    :param base: modulo base of the residue class
    :return: shortest distance between a and b in the residue class
    
    Examples:
    >>> cyclic_distance(2, 1, 10)
    1
    >>> cyclic_distance(2, 9, 10)
    3
    >>> cyclic_distance(2, 9, 20)
    7

    works as well with arrays:
    >>> cyclic_distance(np.array([2,3]), np.array([9,10]), 20)
    array([7, 7])
    """
    return np.minimum((a-b) % base,
                      (b-a) % base,
                      )

if __name__ == '__main__':
    test()