• ### A rudimentary first linear mixed model fit

During the last two weeks I made some progress on my Google Summer of Code project. The Ruby gem is now capable of fitting linear mixed models. In this short blog post I want to give an example, and compare the results I get in Ruby to those obtained by lme4 in R.

• ### Dissecting lme4's lmer function. Part 3.

This is the final part of my analysis of the function lmer, which is used to fit linear mixed models in the R package lme4. In two previous blog posts, we have seen the general layout of the function lmer, the dealings with the R model formula, and the setting up of the objective function for the optimization (see part 1 and part 2).

• ### Dissecting lme4's lmer function. Part 2.

Last time I started to analyze the function lmer that is used to fit linear mixed models in the R package lme4. I have delineated the general steps taken by lmer, and looked at the employed formula module in more detail. The formula module evaluates the provided R model formula to model matrices, vectors and parameters. The next step is to use these to define the objective function that needs to be minimized, which is the profiled deviance or the profiled REML criterion in this case. The objective function is returned by the function mkLmerDevfun which is dissected in what follows.

• ### Dissecting lme4's lmer function. Part 1.

This blog posts marks the start of my Google Summer of Code project with the Ruby Science Foundation, where I will develop mixed linear models software for Ruby. As a preparation for my GSoC project, I will dedicate a couple of blog posts to a meticulous analysis of lme4 code (so that I can steal all the ideas from it!).

• ### Solve two-point boundary value problems in Ruby with spitzy

A few days ago I programmed a numerical method for the solution for two-point boundary value problems, and today I discovered that I can use MathJax to display mathematical formulas in here (although there are some inconveniences related to the use of underscores). So, here goes another blog post!

• ### Solve ODEs in Ruby with spitzy

Over the weekend I have written a couple of numerical solvers for one-dimensional initial value problems in Ruby, and added them to my project spitzy.

• ### Solve an advection equation in Ruby with spitzy

A couple of days ago I started working on a collection of numerical methods for differential equations, wirtten in pure Ruby (I have conviced the professor of my numerical DE class that thats a good idea for my final project in said class).

Recently I got surprised by the behaviour of #permute_columns` in the Ruby gem NMatrix.