def pca_explained_variance_ratio_(pArray, iComponents=1):
    """
	 Input: N x D matrix 
	 Output: D x N matrix 
	
	 """
    from sklearn.decomposition import PCA
    pPCA = PCA(n_components=iComponents)
    pPCA.fit(pArray.T)
    return pPCA.explained_variance_ratio_
