Horst Beyer (left) and Denis Pollney (right) take a break from black holes.

Cactus was originally designed as a framework for physicists with largescale applications which, to model complex natural phenomena with adequate fidelity, need the kind of computational resources only supplied by the world's largest supercomputers.

One important design requirement has been to ensure that the physicists developing and running their simulations had a common working environment. Their codes should be able to be developed and debugged on local laptops and workstations, and then be immediately run on any final production machine ... whether it be a Linux cluster, a Cray T3E or any other supercomputer.

The Lemieux Terascale Computing System at PSC is equivalent to 100,000 iPAQ Pocket PCs.

Other of our recent news items describe how Cactus has been used for simulations running across thousands of processors distributed across several machines ... here we go to the other end of the spectrum ... and describe how Cactus can be run on a iPAQ Pocket PC from HP, one of the latest generations of PDAs.

Physicists Horst Beyer and Denis Pollney, from the Numerical Relativity Group at the Max Planck Institute for Gravitational Physics in Germany, are more used to working with machines at the other end of the Compaq product line. One of the groups main resources is the 3000 processor Compaq Alphaserver "Terascale Computing System" called Lemieux at the Pittsburg omputing Center in the USA, currently the 3rd fastest computer in the world.

xgraph showing data from the simulation (click for fullsize image)

Swapping this 6 Teraflop, 3 TeraByte monster machine for a pocket sized 206 Megaflop, 32 MegaByte iPAQ 3630 Pocket PC, the duo compiled and ran a Cactus application, using the Intimate Linux Distribution, graphing the output data also on the handheld with the xgraph graphics package.

To compare this to Lemieux, 100000 iPAQ Pocket PCs would be needed to provide the same amount of computing power as the supercomputer. At todays prices buying these would cost around $50 Million.

Using a Linux distribution on the iPAQ Pocket PC meant that porting the the Cactus code and the xgraph graphics package was relatively straightforward. Although they used a simple WaveToy application for this example, most of Cactus thorns written in C, C++, or F77 could have been used. (As yet there is no F90 compiler).

While it certainly isn't planned yet to start running black hole simulations on handhelds, physicists do want to start using such devices to complement their high-performance computing work.

The Cactus WaveToy application (click for fullsize image)

With the monitoring and steering web interfaces which can be used with any remotely running Cactus simulation, physicists can use their handhelds, connected wireless to the internet, to interact with their simulations whereever they happen to be. From a web browser on the handheld, they can check on all their simulations, visualize output data, change parameters, and stop and restart them as necessary.

Running Cactus on an iPAQ Pocket PC also demonstrates the emerging Grid-orientated view for HPC ... portable applications can make effective use of all of the computing resources available to their users. Intelligent resource brokers and schedulers can send tasks to the most appropriate machines for execution, taking into account factors such as cost, efficiency, and time to completion. Grid-enabled applications can migrate from resource to resource, spawning subtasks to smaller machines. In this picture a users iPAQ Pocket PC is just another, albeit small, available resource.

Cactus is a main application for the European GridLab project, which contains a whole workpackage on mobile computing using on a range of devices including laptops and iPAQ Pocket PCs.

Initimate Linux Installation:

On the Microdrive:

Using some Linux distribution on a notebook make two partitions on the microdrive using fdisk. The first should be an ext2 partition (83) and the second a swap partition (82) of about 30 MB. (< 32 MB for stability reasons)

fdisk /dev/hde

Format the first partition using reiserfs and make swap on the second:

mkreiserfs /dev/hde1
mkswap /dev/hde2

Boot into familiar.

Install the reiserfs modules:

ipkd install reiserfs-modules-2.4.18-rmk3

Download and install the package intimateboot_0.5-1_arm.ipk from intimate at http://intimate.handhelds.org/install.shtml

ipkg install intimateboot_0.5-1_arm.ipk

cp /linuxrc /linuxrc.familiar
cp /linuxrc.intimate /linuxrc

To enable detection of the Microdrive during startup add the line

sleep 10

in /linuxrc below the line where cardmgr is called (in two places). Run the command

mkdir -p /tmp/intimate && cd /tmp/intimate && wget http://intimate.handhelds.org/installer/installer && sh installer

in a terminal window and follow the install instructions on http://intimate.handhelds.org/install.shtml

Then, finally, you should have a working dual boot system. The Familiar Linux Distribution on the iPAQ Pocket PC and the Linux Intimate Distribution on the Microdrive. Reboot and follow the on screen instructions on your iPAQ Pocket PC to boot into intimate or familiar.

Cactus and xgraph Installations:

To build cactus and xgraph you may need to install g++ and a couple of the X libraries. It is also useful to have CVS for easy downloading. These were installed using

apt-get install g++ xlibs xlibs-dev cvs

Cactus and xgraph can then be downloaded using CVS (or use a tarfile with the distribution described here).

The executables are built in the usual way. For Cactus, this means changing into the Cactus directory and typing

gmake wave-config
gmake wave

To run the created executable, type

cp arrangements/CactusWave/WaveToyC/par/wavetoyc_rad.par exe
cd exe
./cactus_test wavetoyc_rad.par

This will create output in the wavetoyc_rad subdirectory. To visualize this output, compile xgraph in its source directory

xmkmf
make

The executable will be called xgraph. It's useful to put it in a visible place, like /usr/local/bin

Finally, you can plot your data using for example

xgraph wavetoyc_rad/phi.xl