February 2, 2023

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A crucial computer program for particle physics is in danger of becoming obsolete

Recently I saw another particle physicist talking about a calculation he had taken to a new level of precision. His tool? A computer program from the 1980s called FORM.

Particle physicists use some of the longest equations in all of science. For example, to look for signs of new elementary particles in collisions at the Large Hadron Collider, they draw thousands of pictures, called Feynman diagrams, that represent possible collision outcomes, each encoding a complicated formula that can be millions of terms long. Summarizing formulas like this with pen and paper is impossible; even adding it with computers is a challenge. The algebra rules we learn in school are fast enough for homework, but they’re shockingly inefficient for particle physics.

Programs called computer algebra systems strive to accomplish these tasks. And if you want to solve the world’s biggest equations, one program has stood out for 33 years: FORM.

Developed by Dutch particle physicist Jos Vermaseren, FORM is an important part of the particle physics infrastructure required for the most difficult calculations. However, as with a surprisingly large number of essential pieces of digital infrastructure, the maintenance of FORM rests largely on one person: Vermaseren himself. And at 73, he has begun to retire from FORM development. Due to the incentive structure of science, which rewards published articles and not software tools, no successor has emerged. If the situation doesn’t change, particle physics could be forced to slow down dramatically.

FORM began in the mid-1980s when the role of computers was rapidly changing. Its predecessor, a program developed by Martinus Veltman called the Schoonschip, was released as a specialized chip that you plugged into the side of an Atari computer. Vermaseren wanted to create a more accessible program that could be downloaded by universities around the world. He started programming it in the computer language FORTRAN, which stands for Formula Translation. The name FORM was an allusion to this. (He later switched to a programming language called C.) Vermaseren released its software in 1989. By the early 1990s, over 200 institutions around the world had downloaded it, and the number continued to grow.

Since 2000, an article on particle physics citing FORM has been published on average every few days. “Most of them [high-precision] Results that our group has achieved over the past 20 years have relied heavily on FORM code,” said Thomas Gehrmann, professor at the University of Zurich.

Part of FORM’s popularity came from specialized algorithms developed over the years, such as B. a trick for multiplying certain parts of a Feynman diagram quickly and a technique for rearranging equations to have as few multiplications and additions as possible. But the oldest and most powerful benefit of FORM is how it handles memory.

Just as humans have two types of memory, short-term and long-term, computers have two types: primary and external. Main memory – your computer’s working memory – can be accessed quickly, but is limited in size. External storage devices such as hard drives and solid state drives hold much more information but are slower. To solve a long equation, you need to store it in main memory so that you can work with it easily.

In the 1980s, both types of memory were limited. “FORM was built at a time when there was almost no memory and no disk space either – basically nothing,” said Ben Ruijl, a former student of Vermaseren and FORM developer who is now a postdoctoral fellow at the Swiss Federal Institute for Research and teaches Technologie Zürich. This presented a challenge: equations were too long for main memory. To calculate one, your operating system had to treat your hard drive as if it were also main memory. The operating system, not knowing how big your equation should get, stored the data in a collection of “pages” on disk and frequently switched between them as different parts were needed – an inefficient process known as swapping.

This xkcd comic illustrates the situation well.

Image: xkcd.com

FORM bypasses swapping and uses its own technique. When you work with an equation in FORM, the program allocates a fixed amount of disk space for each term. This technique makes it easier for the software to keep track of where the parts of an equation are. It also makes it easy to bring those pieces back into main memory when they’re needed without accessing the rest.

Memory has grown since FORM’s inception, from 128 kilobytes of RAM in the Atari 130XE in 1985 to 128 gigabytes of RAM in my souped-up desktop—a million-fold improvement. But the tricks developed by Vermaseren remain crucial. As particle physicists sift through petabytes of data from the Large Hadron Collider in search of evidence of new particles, their need for precision and, with it, the length of their equations grows longer.