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Why physicists still use Fortran (2015)

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Re: Why physicists still use Fortran (2015)

#171

Post by brei »

dsacco wrote: post #157
ptero wrote: post #150

Earlier quoted context omitted.

Yes, C++ does not buy you that much. Sure, it is a more modern language, but when used by scientists (not software engineers) the advantages are hardly earth shattering. Much of complexity is hidden (as it should be) into libraries. IMO, Python stands a better chance of breaking the Fortran's lock on physics related computing. Give it a few more years and enough numpy-based libraries might make Python a real competit…

I have to be honest with you, as someone who writes in both C++ and Python, I really do not see Python being more of a candidate than C++ for displacing Fortran. Can you clarify why you think Python might be able to do it? For scientific computation with high performance requirements, Python is not competitive with Fortan or C++. For work that continues to happen in Fortran due to "academic inertia", my impression (a…

I don't see Python displacing Fortran or C++, but I do see Python showing up in HPC as a platform for DSLs. Instead of handling the expensive part of the computation, Python acts as a UI layer / configuration manager / code generator. For an example, see fenics: [https://fenicsproject.org/]

Re: Why physicists still use Fortran (2015)

#172

Post by blacksmythe »

LeifCarrotson wrote: post #164
osteele wrote: post #112

Earlier quoted context omitted.

"Within a month of his arrival, Randy solved some trivial computer problems for one of the other grad students. A week later, the chairman of the astronomy department called him over and said, “So, you’re the UNIX guru.” "At the time, Randy was still stupid enough to be flattered by this attention, when he should have recognized them as bone-chilling words. Three years later, he left the Astronomy Department without…

I am unfamiliar with the passage. But it describes two options: 1. "A staggeringly comprehensive knowledge of UNIX", three years of domain-specific education, and a network of people who trust you to--no, who depend on you to be able to get things done with that knowledge 2. A piece of paper just like everyone else in the department. And while the former might be more difficult to make use of, I think it could be muc…

A good point, but the text suggests there are ways to get this knowledge.

  >> except six hundred dollars in his bank account

Re: Why physicists still use Fortran (2015)

#173

Post by WalterBright »

scottlegrand2 wrote: post #74
sidlls wrote: post #26

Earlier quoted context omitted.

Yep. Most of my programming classes were either in pascal or c when I was in undergrad, but in my physics courses, all the way through my graduate education, I used FORTRAN. It's because physics doesn't change that much over the years, FORTRAN code that is time-tested and that works exists and there's no need to re-invent the wheel in another language when more interesting and important problems exist to solve.

David Baker's Rosetta code, which made him a pile of money, is IMO a spectacular example of craptastic C++ written by people who really didn't understand C++ but didn't let that deter them from using every single feature of the language, badly. Some years back we tried to port it to CUDA but there were so many levels of indirection, dereferencing, and virtual functions that it was nearly impossible to make any progre…

> using every single feature of the language

I constantly run into code where someone takes an obscure corner case in the language, and builds an entire edifice around it.

Re: Why physicists still use Fortran (2015)

#174

Post by ehsankia »

smcdow wrote: post #50

Speaking from a government contracting point of view: Nobody is going to pay you to rewrite existing code that's already working. Nobody. The customer doesn't give a flying shit about the implementation. He'd be happy with a box of diodes as an implementation, as long as it worked and came in on time and on budget. When you're writing up your proposal for a contract or a grant, the theme should always be that you're…

As with any sort of big transition (changing e-mail, using a new password manager, changing programming language), the solution is always to do it incrementally.

For e-mail, I generally create a new one, and over a year or two, I create new accounts with the new e-mail and gradually move accounts until the old one is seldom used. Similarly here, it may be a bit tricky, and it really depends on how intertwined it all is, but gradually writing new pieces that you're adding in a new language, or using C++ for pieces that you're rewriting. eventually you'll be much closer than trying to do it all at once.

Re: Why physicists still use Fortran (2015)

#175

Post by DannyBee »

ptero wrote: post #169
dsacco wrote: post #157

Earlier quoted context omitted.

I have to be honest with you, as someone who writes in both C++ and Python, I really do not see Python being more of a candidate than C++ for displacing Fortran. Can you clarify why you think Python might be able to do it? For scientific computation with high performance requirements, Python is not competitive with Fortan or C++. For work that continues to happen in Fortran due to "academic inertia", my impression (a…

A disclaimer -- I do not work in physics, however a couple of recent physics Ph.D. that I work with expressed similar views. Speed is not nearly as important now as it was 10-15 years ago. A typical scientist's worstation has 20 CPU cores. If I want to use 100 CPUs for a few days, it is trivial and 1000 is easy to get. Thus the fact that Python is slow(er) does not bother me unless I am setting up something major . W…

"Speed is not nearly as important now as it was 10-15 years ago." Please try telling that to other users sometime. They do not seem to agree.

Re: Why physicists still use Fortran (2015)

#176

Post by PoachedSausage »

osteele wrote: post #112
thicknavyrain wrote: post #24

"Professors usually have this legacy code on hand (often code they wrote themselves decades ago) and pass this code on to their students. This saves their students time, and also takes uncertainty out of the debugging process." This is so true. I'm a PhD student in physics using Fortran for pretty much that reason. At the start of my PhD, in response to my supervisor telling me I should learn Fortran to modify our cu…

"Within a month of his arrival, Randy solved some trivial computer problems for one of the other grad students. A week later, the chairman of the astronomy department called him over and said, “So, you’re the UNIX guru.” "At the time, Randy was still stupid enough to be flattered by this attention, when he should have recognized them as bone-chilling words. Three years later, he left the Astronomy Department without…

Don't forget his girlfriend.

To paraphrase: "Usually a comprehensive knowledge of UNIX and a girlfriend are mutually exclusive."

Re: Why physicists still use Fortran (2015)

#177

Post by robotresearcher »

thicknavyrain wrote: post #45
PascLeRasc wrote: post #36

Earlier quoted context omitted.

That was without a doubt pretty bad for those grad students' careers. That kind of work shouldn't have been done by anyone without tenure.

I might actually disagree on this one. If it was the first year of their PhD, then yes, it does seem like grunt work which is dissatisfying, but they will have fully learned the ins and outs of their group's code framework. In the process, they would have understood nearly every approach taken by the group towards producing the results that it does, and I bet that has helped them when they've ended up modifying that…

Or you could spend the time reading the papers of many groups.

Re: Why physicists still use Fortran (2015)

#178

Post by felipemnoa »

thicknavyrain wrote: post #24

"Professors usually have this legacy code on hand (often code they wrote themselves decades ago) and pass this code on to their students. This saves their students time, and also takes uncertainty out of the debugging process." This is so true. I'm a PhD student in physics using Fortran for pretty much that reason. At the start of my PhD, in response to my supervisor telling me I should learn Fortran to modify our cu…

>>I later learnt one of our "rival groups" attempted the same thing and it took three phd students working full time for a year to rewrite their code from fortran to C++.

I wonder if there are any transcoders for Fortran to C++? I wonder if there is even a market for something like that? I've written alpha versions of transcoders for C to Java and Java to Objective-C and I think I could do the same for Fortran to another language but why?

Writing a transcoder first is the right way to do it and it should take you a couple of months to do it, especially if you already have some experience with this kind of stuff. Definitely less than a year for a single person. I would not try to translate the code by hand. It would be a never ending project full of bugs.

Edit: Apparently there are plenty of Fortran to C++ transcoders. Here is just one I found during my google search: http://cci.lbl.gov/fable/

No idea how good they work.

Re: Why physicists still use Fortran (2015)

#179

Post by robotresearcher »

bluedino wrote: post #115
thicknavyrain wrote: post #24

"Professors usually have this legacy code on hand (often code they wrote themselves decades ago) and pass this code on to their students. This saves their students time, and also takes uncertainty out of the debugging process." This is so true. I'm a PhD student in physics using Fortran for pretty much that reason. At the start of my PhD, in response to my supervisor telling me I should learn Fortran to modify our cu…

>> Professors usually have this legacy code on hand (often code they wrote themselves decades ago) and pass this code on to their students So cut-n-paste code. The students are running code that they don't really know what it does, it might not even be correct...it's like StackOverflow in academia.

Did you write your own libc and libm? Compiler? We are ALL using code we didn't write.

Re: Why physicists still use Fortran (2015)

#180

Post by ptero »

serf wrote: post #39
thicknavyrain wrote: post #24

"Professors usually have this legacy code on hand (often code they wrote themselves decades ago) and pass this code on to their students. This saves their students time, and also takes uncertainty out of the debugging process." This is so true. I'm a PhD student in physics using Fortran for pretty much that reason. At the start of my PhD, in response to my supervisor telling me I should learn Fortran to modify our cu…

His response was "You could do that and it would probably be enough to earn your PhD, since it'll take you at least three years. But I suspect you'll want to work on something else during that time". as someone who had contact with that codebase, do you have any insights as to why that is? Was it the sheer size of the thing? Was it some nuance that Fortran had as an advantage over other languages? was the math just d…

To do such a rewrite one needs domain knowledge much more than you need software engineering knowledge. This means you need to get research physicist to contribute major effort into such a rewrite. To get there one needs to make them see a clear benefit of translating a system (that works fine today, thank you), from language A to language B.

A Ph.D. student or a young researcher might be more interested if a rewrite lets them run experiments using Amazon / CUDA / whatever for a few thousand dollars instead of spending scarce grant money on dedicated hardware.

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