Laurence McGlashan

First Chinese (中文) Blog Post

2011-12-24T00:00:00+00:00

你好, 我叫劳伦思。我学说中文。

我	I
你	you
好	good
叫	called
劳伦思	Laurence
学	learn
说	speak
中文	Chinese

Writing Dimensional Units in LaTeX

2011-08-17T00:00:00+00:00

This is some useful LaTeX code to make adding SI dimensional units to quantities much easier:

\newcommand{\dimensions}[5]{\ensuremath{\
    \ifthenelse{\equal{#1}{0}}{}{\ifthenelse{\equal{#1}{1}}{\text{kg}\ }{\text{kg}^{#1}\ }}%
        \ifthenelse{\equal{#2}{0}}{}{\ifthenelse{\equal{#2}{1}}{\text{m}\ }{\text{m}^{#2}\ }}%
            \ifthenelse{\equal{#3}{0}}{}{\ifthenelse{\equal{#3}{1}}{\text{s}\ }{\text{s}^{#3}\ }}%
                \ifthenelse{\equal{#4}{0}}{}{\ifthenelse{\equal{#4}{1}}{\text{K}\ }{\text{K}^{#4}\ }}%
                    \ifthenelse{\equal{#5}{0}}{\!}{\ifthenelse{\equal{#5}{1}}{\text{kmol}}{\text{kmol}^{#5}}}}}

You can then define shortcuts to make things even easier:

\newcommand{\dimT}{\dimensions{0}{0}{0}{1}{0}}
\newcommand{\dimWatt}{\dimensions{1}{2}{-3}{0}{0}}
\newcommand{\dimJoule}{\dimensions{1}{2}{-2}{0}{0}}
\newcommand{\dimPascal}{\dimensions{1}{-1}{-2}{0}{0}}

OpenFOAM-2.0 Released

2011-06-17T00:00:00+00:00

"OpenFOAM-2.0":http://www.openfoam.com has been released, and there are lots of exciting "new features":http://www.openfoam.com/version2.0.0! I'm happy to say that the "Git repository":http://www.openfoam.com/download/git.php installs on Fedora 15 smoothly. The namespace storing math constants had changed, so to update all the namespace declarations in my own code I ran the following:

grep -lre 'mathematicalConstant::' . | xargs -d'\n' sed -i 's/mathematicalConstant::/constant::mathematical::/g'

Hope that helps some of you.

Eclipse Helios and Fedora 14

2010-11-08T00:00:00+00:00

I found that the C++ indexer in Eclipse Helios crashed the application in Fedora 14. Obviously this was slightly annoying if I want to use it as an IDE... Anyway, apparently it's due to Java, and there's a simple hack here to get it working: "Eclipse CDT indexer crashes in Fedora 14":https://bugzilla.redhat.com/show_bug.cgi?id=647737 In essence, just add the following to /etc/eclipse.ini:

-XX:-UseCompressedOops

This is just a quick fix: They're continuing to find a proper solution.

RADAU ODE Solver for OpenFOAM

2010-10-01T00:00:00+00:00

Download RADAU Patch

Here's a patch for OpenFOAM to add RADAU as an ODE solver. Simply apply the patch to create a folder within /src/ODE/ODESolver called RADAU, then remake the folder ODE using `wmake libso'. You can test RADAU using /applications/test/ODETest. Here's how it roughly performs to SIBS: RADAU: Analytical: y(2.0) = 4(0.223891 0.576725 0.352834 0.128943) Numerical: y(2.0) = 4(0.223891 0.576725 0.352834 0.128943) SIBS: Analytical: y(2.0) = 4(0.223891 0.576725 0.352834 0.128943) Numerical: y(2.0) = 4(0.223891 0.576725 0.352833 0.128944) There's still some work to do to integrate it properly. If there's interest let me know or have a go yourself!

Profiling C++ Code

2010-09-02T00:00:00+00:00

Recently I used profiling on some C++ libraries I wrote for use with "OpenFOAM®":http://www.openfoam.org. Profiling allows you to see how much time your program spends inside each function. Using this, within half an hour I managed to reduce the cpu time of the code by around 70%. The offending code was calculating an integral, which contained many uses of the pow() function. The cpu time was easily reduced by precalculating some of these outside the integral and using sqr(x) instead of pow(x,2).
You can use gprof, but all the code needs to be recompiled using the -pg option. Instead you can use Cachegrind or Callgrind which don't require your code to be recompiled. The disadvantage is that they cause the code to run slower.
I used "Callgrind":http://valgrind.org/docs/manual/cl-manual.html, a tool that is part of "Valgrind":http://valgrind.org. It's executed using:

valgrind --tool=callgrind <executableName>
kcachegrind

When the simulation is done you'll see a callgrind file in the current directory. Opening it with "kcachegrind":http://kcachegrind.sourceforge.net/html/Home.html allows you to easily trace through the functions that have been called. You can even generate nice looking call graphs to help you trace function calls:

OpenFOAM/F13 Linking Issue Fixed

2010-08-31T00:00:00+00:00

The issue in post "OpenFOAM Fedora 13 Fork":/openfoam/fedora/2010/08/30/openfoam-fork.html has been fixed in the OpenFOAM-1.7.x repository. Fedora's Gcc has implicit linking turned off. To turn it back on again add the following option to g++:

-Xlinker --add-needed

OpenFOAM Fedora 13 Fork

2010-08-30T00:00:00+00:00

I have forked "OpenFOAM":http://www.openfoam.org for Fedora 13. This is because Fedora 13 no longer allows implicit linkage (see "DSO Link Changes":http://fedoraproject.org/wiki/UnderstandingDSOLinkChange).

A fix is to change the relevant Make/options files from

EXE_INC = \
    -I$(LIB_SRC)/finiteVolume/lnInclude

EXE_LIBS = -lfiniteVolume

EXE_INC = \
    -I$(LIB_SRC)/finiteVolume/lnInclude

EXE_LIBS = -L$(FOAM_MPI_LIBBIN) \
           -lPstream \
           -lfiniteVolume

First Blog Post

2010-08-28T00:00:00+00:00

This is the first blog post. Below I have tried out some C++ highlighting:

for (int i=0;i<Nf;++i)
{
    rho += alpha[i]*mtm.rhod(i);
}