Monday, June 27, 2011

SPH in movies

Superman returns – but who’s looking after his water?

Is it a plane? No, it’s Smoothed Particle Hydrodynamics.
William West/AFP

Watching films such as Superman Returns or The Day after Tomorrow, you would have seen dramatic sequences of surging water and crumbling buildings.

While doing so, mathematics was probably the last thing you thought about; but without it, scenes of this nature would be virtually impossible.

Take the 2006 film Superman Returns. In one scene, a giant spherical object smashes into a water tank releasing a huge amount of water (see below).

Still image from Superman Returns. Courtesy of Sony Pictures Imageworks

Traditionally, the only possible way to create this kind of sequence would be to use small models – which produce unrealistic results. Or we could create a computer simulation.

Swapping droplets for particles

These days, one of the most popular methods for simulating water is to replace fluid with millions of individual particles within a computer simulation.

And the way these particles move is determined by an algorithm that my colleagues and I invented to simulate the formation of stars in our galaxy’s giant molecular clouds.

The method is known as Smoothed Particle Hydrodynamics (SPH) and the use of SPH in Superman Returns is the work of an American visual effects company called Tweak.

Superman Returns certainly isn’t the only film to feature SPH fluid simulations: think of Gollum falling into the lava of Mount Doom in Lord of the Rings: Return of the King; or the huge alligator splashing through a swamp in Primeval.

These particular scenes are the work of people at a Spanish visual effects company called NextLimit, who received an Oscar for their troubles.

How does SPH work?

Rather than trying to model a body of water as a whole, SPH replaces the fluid with a set of particles. A mathematical technique then uses the position and masses of these particles to determine the density of the fluid being modelled.

Using the density and pressure of the fluid, SPH makes it possible to map the force acting on each particle within the fluid. This technique provides results quite similar to the actual fluid being modelled. And the more particles used in the simulation, the more accurate the model becomes.

This SPH simulation uses 128,000 particles to model a fluid.

Beyond the basics

In Superman Returns, gravity also affects how the body of water behaves (the water spills out of the water tank) and SPH can easily be adapted to accomodate this.

In addition, fluids often need to flow around solid bodies such as rocks and buildings that might be carried, bobbing along, by the flow. The SPH method can be easily extended to handle this combination of solid bodies and fluids by adding sets of particles to the equation, to represent the solid bodies.

These adjustments and extensions to SPH can be made to produce very realistic-looking results.

In industry, SPH is used to describe the motion of offshore rigs in a storm, fluid flow in pumps, and injection moulding of liquid metals. In zoology, it’s being used to investigate the dynamics of fish.

SPH and the stars

As hinted at above, it’s not just water and its inhabitants that can be modelled using this technique.

SPH simulations of star formation by Matthew Bate, from the University of Exeter, and Daniel Price, of Monash, have been able to predict the masses of the stars, and the number of stable two- and three-star systems that form from a typical molecular cloud.

In the case of stable two-star systems (known as binaries) SPH can predict the shape of the orbits in good agreement with astronomical observations.

To get this level of accuracy, millions of particles are used in the SPH calculation, and the motion of these particles is calculated on a number of computer systems that work together in parallel.

SPH is also the method of choice for following the evolution of the universe after the Big Bang. This evolution involves dark matter and gas, and the simulations have one set of SPH particles for the dark matter and one set for the gas.

An advanced SPH code – known as Gadget – used for this purpose was developed by Volker Springel. The code enables astrophysicists to predict the way galaxies form and their distribution in the universe, including the effects of General Relativity.

But for non-astrophysicists, admittedly, the movies may be more of a draw.

So next time you’re watching a film and you see large swathes of water in unusual places or doing incredibly destructive things, think about maths for a moment: without it, such breathtaking scenes would be virtually impossible.

Friday, March 18, 2011


Note to myself:
Quoted from

Contributors are your participants. If there is nothing to contribute, you have no participants. If you have no participants, you barely even have a project, let alone co-development! For FLOSS projects, change has an incentive beyond improving the software.
Readability is the key to creating code that others will use. Because in the end? We can scale silicon, but carbon? People are much harder to scale.

Saturday, March 5, 2011

My new mobile

At long last, i've got a new mobile, after years of using the venerable good old fellow Nokia 1100
My old phone: Nokia N8 (circa 2005)
There was not much wrong with the old phone apart from battery problem. However there was one thing which made me buy new phone earlier.
Earlier last month Nokia announced at MWC its deal with MSFT, and the trojan horse that Elop proved himself. I loved Nokia and was waiting for a long time for the N9 with Meego to come to market. However this announcement quashed all my hopes. Hence i bought a Nokia phone while it was still available w/o Windows OS. And the best Nokia phone in market at the time in India was the Nokia N8.
So this is my new phone, a silver Nokia N8.
My new phone: Nokia N8
Many people have asked my why Nokia instead of Android. Well it has really awesome hardware, even if the software Symbian^3 is not as snappy and does not have a million stupid apps in the Ovi store.
Here are some things which impressed me:
  • 12 MPx camera with carl-zeiss lenses and xenon flash: I can assure you it can take really awesome pics and i know mega-pixels are not everything in photography. It has a really large sensor for a camera phone. Of course it cannot replace a dedicated DSLR camera (i don't have one), but is handy and good as my primary camera.
  • FM Transmitter: Yes you can start your own radio station upto a few meters. Not that i have any idea to use it, but still its a cool technology.
  • USB on the go: I can connect usb storage drives (pen drives and external hard disk drives directly to my mobile). USB keyboard and mouse can also be connected to the mobile.A mouse cursor moving in the mobile looks really cool.
  • Proper wireless and proxy support: My friend's android cannot connect to ad-hoc wireless networks and also does not support proxy on wlan, so the he needs to be connected to gprs.
  • I do not want google to know "ALL" about me.
One con of this mobile is that development on symbian has stopped, and linux support for symbian development is abysmal, and there's no FOSS compiler on linux to compile to symbain, and nokia remote compiler does not support proxy.
If only pyside would work on N8, i'd be really happy. Anyone interested in a GSOC project for this please check here Treat assured :)

Saturday, January 22, 2011

Stay Healthy By Taking Breaks

Stay Healthy By Taking Breaks: "
Most of us lead sedentary lifestyles these days -- most of our time is spent in front of computers. This slowly is causing a lot of problems people from previous generations haven't experienced: back aches, knee problems, wrist pains, myopia, among others. And just going to a gym or putting in one hour of physical activity a day isn't enough. It doesn't help balance the inactivity over the entire day.

I recently wrote an article in the BenefIT magazine that talks about two tools: Workrave and RSIBreak. Thanks to the publishers, the article is available in pdf format under a CC license.

I've tried both the software but have been using Workrave for quite a while now and am quite happy with it. To briefly introduce them: both software prompt the user to take a break at regular intervals. They have timers that trigger at configured intervals asking the user to take a break. Workrave also has some stretching exercises suggested that can be performed in the longer breaks. The shorter (and more frequent) breaks can be used to take the eyes off the monitor and to relax them. Read the article for more details.

I've reviewed Workrave version 0.9.1 in the article, though the current version as of now is 0.9.3, which has a few differences from those mentioned in the article. The prime difference is the addition of a 'Natural Rest Break' that gets triggered when the screen-saver gets activated, which is nice since if the user walks away from the computer for a prolonged period of time, the rest break in effect has been taken, and the next one is scheduled after the configured duration once the screen-saver is unlocked.

Both software are available in the Fedora repository: Workrave is based on the GTK toolkit (and integrates nicely with the GNOME desktop), whereas RSIBreak is based on the Qt toolkit (and integrates nicely with the KDE desktop). Give these software a try for a cheap but effective way of staying healthy!


I've installed Workrave now from the fedora repos. It seems much better than the gnome-typing-break in the keyboard preferences. RSIBreak tries to install a whole lot of KDE dependencies. If anyone of you sits for long hours on a computer, please be nice to yourself and prevent RSI (repetitive strain injury) and other such problems. If you think that working out a few hours in gym will counter it, you are mistaken.

Tuesday, January 18, 2011

firefox 4b9

Firefox 4 beta 9 is looking good, apart from no hw acceleration on linux.
The minizable menu-bar is a very cool feature. Now all the UI is reduced to a single line on my firefox :)

Here's a screenshot running firefox 4b9 on gnome-shell. See how the menu, back-forward buttons, awesomebar, tabs, tabs-list, panorama all fit into a single line. Now thats some use of the wide laptop screens.

Mathematics, History and worms eating manuscripts…

Mathematics, History and worms eating manuscripts…: "

This is a sad story of forgetten history, indifference towards ancient knowledge and wisdom & callous neglect…Read on.. From A search for India’s mathematical roots, some depressing excerpts (emphasis added):

K. Ramasubramanian is the head of the Indian Institute of Technology, Bombay (IIT-B) research Cell for Indian Science and Technology in Sanskrit (CISTS), the only one of its kind in the country, where doctoral students translate the work of ancient Indian scientists into English, study language technology in Sanskrit that will help computers to analyse a wide range of speech and text, and make the translation and interpretation of Sanskrit texts easy.

…“No country should allow the distortion of its own history,” said Murli Manohar Joshi, former Union minister for human resource development, who had directed all the IIT campuses to set up a CISTS in 2002. Following the directive, IIT-B appointed Kulkarni to spearhead research in Sanskrit language technology in 2003. A year later, the institute brought Ramasubramanian on board.

His students are now at different stages of translating primary Sanskrit texts (dating between the seventh and 15th centuries) of the Kerala School mathematics…All these texts work on the same principles, but work on different timescales. For instance, “Siddhanta texts help predict astronomical positions for a mahayuga (great age), which is about 4,320,000 years. The intermediate Tantra texts work with a yuga, one-tenth of that time—432,000 years. Finally, the Karna texts help quick calculations for as little as one month. My students are working with all three of these texts,” said Ramasubramanian.

…But not every member of the team has scientific training. One of them is a trained astrologer and delighted to read the future. Dinesh Mohan Joshi, (grandson of an astrologer) said: “I saw my grandfather look at kundalis (a graphical representation of planetary positions at birth that charts the life course of the baby) and makes predictions. I saw them come true. I was fascinated. I wanted to be able to do that too. So, I went to (Shri) Lal Bahadur (Shastri) Sanskrit Vidyapeeth, Rashtriya Sanskrit Vidyapeeth and became an acharya (teacher) there. Then a friend told me about this cell and I decided to come.” Unlike Bhatt, his was an uphill struggle to master the mathematics, “because I had no formal training in the subject”.

…And in Joshi’s struggle to learn mathematics, lies the biggest challenge that this venture faces, because “there just aren’t enough people who are skilled in both. If they know Sanskrit, they know little science. And if they are good scientists, they are not interested in Sanskrit or translation of Indian texts”, said Subramanian, explaining why, despite making an enormous effort, IIT has not been able to expand the cell.

Photograph of K. Ramasubramanian, courtesy: IIT Mumbai

Another challenge is of a different nature: Original manuscripts are either rotting or missing. “I had gone to find out some text related to my research at the Kerala University library of manuscripts when I found worms eating four of seven manuscripts. I bought lemongrass oil and gave it to the librarian who said they were too short staffed to look after the documents,” said Ramasubramanian, lamenting that it was the same story across the country. “We simply do not take our historical heritage, intellectual heritage seriously.”

The professors and students say they have to battle for respect in a country where history, especially the history of science has little value. “Only recently, the cell has started getting more visibility, people have begun asking us to come and talk about our work. Slowly, people are becoming interested…” Kulkarni said.

Reminded me of: Does no one remember the Hindu contribution to Mathematics? and this on the Kerala School