[OctDev] econometrics functions

[Michael C. <mic...@ua...>]

Hello,

I've added functions for maximum likelihood estimation to the directory 
main/econometrics. The functions need the addition of help messages, but for 
now there is the script mle_example.m, which shows how to use the set of 
functions.

The basic thing a user needs to do is define the log-likelihood function for a 
model using the framework

function log_likelihood = my_likelihood(theta, data, otherargs)
< lines to calculate log_likelihood>
endfunction

or optionally 

function [log_likelihood, score] = my_likelihood(theta, data, otherargs)
< lines to calculate log_likelihood and score>
endfunction


In this framework:

* theta is a kX1 parameter vector

* data is an nXp matrix

* log_likelihood is an nX1 vector of log-likelihood contributions

* score is and nXk matrix of score contributions, the derivatives of the rows 
of log_likelihood w.r.t the transpose of theta


Otherargs is whatever else is needed to calculate the likelihood function. It 
may be an empty place holder.

Comments welcome. I'm planning to add similar functions for GMM estimation 
soon.

Michael