# fa.bianp.net

A little experiment to see what low rank approximation looks like. These are the best rank-k approximations (in the Frobenius norm) to the a natural image for increasing values of k and an original image of rank 512.

Python code can be found here. GIF animation made using ImageMagic's convert …

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 …

As a warm-up for the upcoming EuroScipy-conference, some of the scikit-learn developers decided to gather and work together for a couple of days. Today was the first day and there was only a handfull of us, as the real kickoff is expected tomorrow. Some interesting coding happened, although most of …

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 …```

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 …

I was last weekend in FOSDEM presenting scikits.learn (here are the slides I used at the Data Analytics Devroom). Kudos to Olivier Grisel and all the people who organized such a fun and authentic meeting!

I've been working lately with Alexandre Gramfort coding the LARS algorithm in scikits.learn. This algorithm computes the solution to several general linear models used in machine learning: LAR, Lasso, Elasticnet and Forward Stagewise. Unlike the implementation by coordinate descent, the LARS algorithm gives the full coefficient path along the …

En la ciudad fabrican a las personas en serie. En el campo, los siguen haciendo a mano: los moldean, los secan al sol y luego los pintan, por eso son tan especiales. Primer concierto de la nueva gira en Mengíbar, y uno de los fines de semana más intensos que …

Por fin encontré la manera para no dejarme la vista intentando distinguir azul oscuro sobre negro. Se trata de añadir el código a tu .bash_profile y los directorios se te colorearán de un verde mucho más legible alias ls='ls --color' LS_COLORS='di=1:fi=0:ln=31:pi=5 …

Después del concierto en Sevilla, fin de semana esclavo grabando en Daimiel, en La Mancha. Era mi primera vez grabando con Los Esclavos, y la verdad es que la cosa no pudo salir mejor, sonando bien y del tirón, sin mayores complicaciones. Al final serán 4 canciones que se colgarán …