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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _to_tonnetz(chromagram):
 """Project a chromagram on the tonnetz. Returned value is normalized to prevent numerical instabilities. """

    if np.sum(np.abs(chromagram)) == 0.:
        # The input is an empty chord, return zero. 
        return np.zeros(6)
    
    _tonnetz = np.dot(__TONNETZ_MATRIX, chromagram)
    one_norm = np.sum(np.abs(_tonnetz))  # Non-zero value
    _tonnetz = _tonnetz / float(one_norm) # Normalize tonnetz vector
    return _tonnetz