(C) Common Dreams
This story was originally published by Common Dreams and is unaltered.
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Google just smashed the world record for calculating digits of pi [1]
['Condé Nast', 'Sanjana Varghese']
Date: 2019-03-14 07:00:00+00:00
Iwao used 25 virtual machines to carry out those calculations. “But instead of clicking that virtual machine button 25 times, I automated it,” she explains. “You can do it in a couple of minutes, but if you needed that many computers, it could take days just to get the next ones set up.” Iwao ran y-cruncher on those 25 virtual machines, continuously, for 121 days.
In order to make sure nothing went wrong, the virtual machines had to be running constantly. Just like a calculation by hand, or on a whiteboard, every step had to be clearly visible, something which would only be possible if the cloud kept the program continuously running. “You can’t take a nap and then start over when you’re doing it by hand, so you have to store all the data necessary to do the math,” says Iwao. “So, with pen and paper, you need a lot of sheets of paper. In this case, you need a lot of storage.” She also set up a monitoring system, which would alert her if something had gone wrong – for example, if one of her virtual machines had suddenly crashed. Just one crash – even for a couple of minutes – could have jeopardised the whole process.
“Y-cruncher, and Google Cloud, both have these methods of making copies – so it’s like photocopying at certain points, and I set it up so that you can take copies of these disks instantly without stopping the calculation,” says Iwao. That data is then copied and saved externally, on other discs, as snapshots.
“There were a couple of parametres I did tweak at the beginning, like how much data you could read or write at one time, and how the boundaries would change as it got bigger,” says Iwao.
As the calculations became increasingly complex, the greater the strain it was on the virtual machines, and the more time it took. Y-cruncher’s calculations don’t work at a linear rate – if you wanted to calculate twice as many digits, it takes more than twice as much time and storage, which proved difficult when Iwao was making the initial calculations, to figure out how many virtual machines she would need.
But the real pressure came closer to the end. Built into y-cruncher are two base algorithms – one for the calculations of pi itself, and another for the verification. The verification algorithm runs alongside the calculation, but it only calculates one single digit of pi, and it takes a lot of time and resources. So you couldn’t use the verification program to calculate every single digit, because it would simply take even more time and storage. What it can do is prove that your results are correct. “The final multiplication is important, because if you miss one digit during those calculating processes, then the entire result is wrong,” says Iwao.
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[1] Url:
https://www.wired.co.uk/article/google-computing-pi-maths
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