feature_scaling

import numpy as np
# z-score normalization 
def zscore_normalize_features(X):
    """
    computes  X, zcore normalized by column
    
    Args:
      X (ndarray): Shape (m,n) input data, m examples, n features
      
    Returns:
      X_norm (ndarray): Shape (m,n)  input normalized by column
      mu (ndarray):     Shape (n,)   mean of each feature
      sigma (ndarray):  Shape (n,)   standard deviation of each feature
    """
    # find the mean of each column/feature
    mu     = np.mean(X, axis=0)                 # mu will have shape (n,)
    # find the standard deviation of each column/feature
    sigma  = np.std(X, axis=0)                  # sigma will have shape (n,)
    # element-wise, subtract mu for that column from each example, divide by std for that column
    X_norm = (X - mu) / sigma      

    return (X_norm, mu, sigma)