## 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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## Useful Tips on Running External Programs from Matlab on Linux

Most of these problems stem from bad association of Matlab’s C++ (or Fortran) libraries. The solution is often to create a soft-link and point to the corresponding system libraries. This blog article provides a very nice summary of this!

Matlab: Running External Programs

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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

## Segmentation error – another quarrel with Matlab

Or: the painful journey to shift into 64-bit era!

Matlab 2009a made radical changes such that all mex functions calling BLAS and LAPACK libraries assume 64-bit integers (instead of 32-bit) on 64-bit system. This means lots of mex functions before this need to be upgraded to run properly, otherwise checked with segmentation failure. It so happened I encountered this today, and cried with my workstation several hours, and turned down by the fact the fixes provided by Matlab seem not working.