Category Archives: Programming

Math bits from a computational blog

This blog (“Walking randomly”) contains a pretty host of good pieces in computational programming, in Matlab, Python, R, etc, and also of news about computational software, particularly open-source tools, and mathematics by large.

Several that are of interest to most (after a very random walk of recent entries):

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CVX Annouced Version 2 (beta)

CVX has become an indispensable tool for modeling and prototyping in various scientific disciplines, in particular where optimization play significant roles.  It provides a most intuitive modeling interface that bridges complex formulation and the underlying numerical solvers, saving the user abundant time for thinking.

Version 2 of CVX has featured extended support for commercial solvers, MOSEK and Gurobi. This is really good news for academic users, since 1) both solvers provide free licenses to academic users; and 2) both solvers are mostly more optimized than the free solvers currently bundles with CVX, namely, SDPT3 and SeDuMi. Related part of the announcement as follows:

  • Academic users may utilize the CVX Professional capability at no charge.
    • Users with a valid academic license for Gurobi 5.0 or later may use it with CVX without obtaining a CVX Professional license. This is because CVX is able to detect the presence of an academic Gurobi license.
    • In order to use MOSEK, a CVX Professional license is required. We intend to provide such licenses at no charge, but we have not yet completed the licensing architecture. We will make an announcement once this has been completed.

In addition, mailing list support has changed into a Q&A forum (StackExchange style …) and the documentation has changed to online html version with better cross references.

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LaTeX to Blogger powered by MathJax (Experimental)

The past weekend I was trying to figure out how to convert \LaTeX source to Blogger compatible sources with the support of the powerful MathJax mechanism to display math.

There’s already an excellent tool (latex2wp) that serves the conversion from \LaTeX to WordPress as I noted before (and best advertised by Terry Tao’s WP blog). But there seem to be numerous legitimate reasons for doing similar thing on Blogger, the most notable one is Blogger allows network scripts to run for the blog (check out the concept of content distribution network, or CDN) and the powerful MathJax engine *happens* to provide such CDN service from recently. If you don’t appreciate why the bother to create yet another math display protocol MathJax, just come down here and have a look at the wonderful demos while imagining what would happen to image-based rendering of math at scaling.

A moment’s research revealed the major difference WordPress and blogger (precisely MathJax) are on handling \LaTeX math: the former uses “$1atex … $” format (I intentionally put the number “1” instead of the letter “l” to avoid invoking the WP interpreter) while the latter just directly the \LaTeX code as “$ … $“. Another major piece lies at how they handle displaying style (vs. the inline style delimited by “$ … $“). WP is to handle the following “<p align=center> $ latex \displaystyle … $ </p>\n“, whereas MathJax can handle “\[ … \] ” directly (“\begin{equation} … \end{equation}” alike are converted to “\[ … \]” with proper numbering). Other minor details are different formats of line breaks and so on.

So I have worked on the latex2wp package directly and made necessary changes as discussed. Some simple tests tell that it’s working fine. Probably you’d like to have a try! (Albeit my great admiration for MathJax and blogger, I have no intention to move to Blogger.com yet since it’ll definitely expend a considerable amount of work. ) Here’s the download link from my dropbox

Latex2Blogger.0.6.2b.tar.gz

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Image Transformations Done Right in Matlab

Though simple and basic, spatial (geometric) transformations in image processing involve lots of subtleties – neglecting these will probably return you awkward results. These subtleties include but are not limited to (esp. in Matlab)

  • Convention in transformation matrices
  • Convention in coordinate axes
  • Position of the input image in the source plane
  • Bounding box calculatio
  • Visible region calculation

Steve  Eddins, a software engineer specialized in image processing, has a series of blog articles devoted to these issues.  He has also contributed a new chapter in the 2nd edition of the classic “Digital image processing using Matlab” (Chapter 6: Geometric Transformations and Image Registration)

Steve on Image Processing

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“Undefined References” Errors in gcc/g++ Compiling

(For C/C++ compiling in Linux-like environments with GCC)

The two probable causes,

1)      External libraries are not completely acknowledged

2)      External libraries are not properly acknowledge Continue reading

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