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Numerical optimizers for Logistic Regression

Category: misc
#machine learning #logistic regression #Python #SciPy

In this post I compar several implementations of Logistic Regression. The task was to implement a Logistic Regression model using standard optimization …

Singular Value Decomposition in SciPy

Category: misc
#python #scipy #svd

SciPy contains two methods to compute the singular value decomposition (SVD) of a matrix: scipy.linalg.svd and scipy.sparse.linalg.svds. In this post I'll compare both methods for the task of computing the full SVD of a large dense matrix.

The first method, scipy.linalg.svd, is perhaps …

qr_multiply function in scipy.linalg

Category: misc
#python #scipy

In scipy's development version there's a new function closely related to the QR-decomposition of a matrix and to the least-squares solution of a linear system. What this function does is to compute the QR-decomposition of a matrix and then multiply the resulting orthogonal factor by another arbitrary matrix. In pseudocode …

Ridge regression path

Category: misc
#scikit-learn #scipy #linear algebra

Ridge coefficients for multiple values of the regularization parameter can be elegantly computed by updating the thin SVD decomposition of the design matrix:

import numpy as np
from scipy import linalg
def ridge(A, b, alphas):
    """
    Return coefficients for regularized least squares

         min ||A x - b||^2 + alpha ||x||^2 …

Computing the vector norm

Category: misc
#linear algebra #norm #scipy

Update: a fast and stable norm was added to scipy.linalg in August 2011 and will be available in scipy 0.10 Last week I discussed with Gael how we should compute the euclidean norm of a vector a using SciPy. Two approaches suggest themselves, either calling scipy.linalg.norm …