Showing posts from September, 2013

NAG Toolbox for MATLAB® documentation for the Mark 24 release

A look at the documentation features in the new, Mark 24, release of the NAG Toolbox for MATLAB®.MATLAB Documentation Help CenterRecent versions of MATLAB have a new documentation system known as the Help Center. This, however is restricted to products from MathWorks; third party extension toolboxes such as our NAG Toolbox for MATLAB® are now documented in a separate help application for Supplemental Software. This has necessitated changes in the way the NAG Toolbox documentation is packaged and installed, and we have taken the opportunity to update the system generally. This post explores some of the new features.Installation DirectoryPrevious releases of the Toolbox have, by default, installed in the toolbox directory of the MATLAB installation on the user's machine. Due to changes in the MATLAB system this does not work for releases after R2012a. So by default the new Mark 24 release of the NAG Toolbox installs under a top level NAG directory in a similar location to our other …

How do I know I'm getting the right answer?

Many recent developments in numerical algorithms concern improvements in performance and the exploitation of parallel architectures. However it's important not to lose sight of one crucial point: first and foremost, algorithms must be accurate. This begs the question, how do we know whether a routine is giving us the right answer? I'm asking this in the context of the matrix function routines I've been writing (these are found in chapter F01 of the NAG Library), but I'm sure you’ll agree that it’s an important question for all numerical software developers to consider. First, it's important to note that the term "the right answer", is a little unfair. Given a matrix A stored in floating point, there is no guarantee that, for example, its square root A1/2 can be represented exactly in floating point arithmetic. In addition, rounding errors introduced early on can propagate through the computation so that their effects are magnified. We'd like to be ab…