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Why physicists still use Fortran (2015)

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Re: Why physicists still use Fortran (2015)

#201

Post by geezerjay »

rxhernandez wrote: post #68
thicknavyrain wrote: post #47

Earlier quoted context omitted.

Pretty much just size! There was about 20,000 lines of it, it's legacy code that has been gradually added to since the 1980s, so it would have taken a while to rewrite all the parts to work with each other. Perhaps some day though.

20,000 lines of code really doesn't seem like that much. I probably output that much in about 2-3 months of biomedical research so there has to be more to it than that.

> 20,000 lines of code really doesn't seem like that much.

Once I spent close to a month hunting down a subtle but nasty bug in a number crunching module which was perhaps around 2k LoC. Writing code is very easy. Verifying and validating number crunching code is very hard and very time consuming.

Re: Why physicists still use Fortran (2015)

#202

Post by fnord123 »

kowdermeister wrote: post #197
scottlegrand2 wrote: post #74

Earlier quoted context omitted.

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…

> which made him a pile of money May I ask how? I don't see ads or any other obvious monetization channels.

Rosetta is a protein folding bit of software: https://els.comotion.uw.edu/express_license_technologies/ros...

GP is not talking about http://rosettacode.org/wiki/Rosetta_Code

Re: Why physicists still use Fortran (2015)

#203

Post by cbcoutinho »

neutronicus wrote: post #42
quadruplebond wrote: post #11

As someone working on an Exascale project for electronic structure calculations, I have a theory about the longevity of Fortran. It's the fact that many of these codes were started years ago and the people who have the credentials and ability to get funding for super computing projects learned on Fortran and stayed with Fortan because they were scientist first and programmers second. Modern Fortran has many nice feat…

Specifically on the topic of HPC, I know of a lot more GPU stuff happening in C/C++ than in Fortran.

I thought Cuda was it's own language, which is accessed by either C or Fortran through bindings

Re: Why physicists still use Fortran (2015)

#204

Post by newen »

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…

More like 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, 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 (and probably a girlfriend)

Re: Why physicists still use Fortran (2015)

#205

Post by guitarbill »

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…

Trusting legacy code with few users is a dangerous proposition. My roommate was given some "state-of-the-art" code and told to run simulations with it. The only graphical output was postscript (for some reason), so every frame was 150 MiB and took minutes to dump - so usually, this was only done at the end to show the result.

I managed to hack in a step which just dumped the memory of resulting frame to a file, and then we wrote a Python script to read that and produces a PNG.

We combine the PNGs into an animation and show someone else in the department because the supervisor wasn't in that day. "Cool! But, hrmm, those boundary conditions look wrong." Sadly, this was 2/3s into his Masters.

Like much now in Physics, the original code was simply incorrect. This happens all the time, and papers get retracted because of it - well, that's the best case if somebody notices.

At the end of the day, programming languages come with eco-systems, and must be chosen solely as a tool. The problem is not with Fortran, but that often Fortran == outdated development practices and in Physics horrible code hacked on by 10+ people without prior programming experience.

Re: Why physicists still use Fortran (2015)

#206

Post by [deleted] »

jxcole wrote: post #89

So the article basically says: 1) Some stuff is already written in Fortran so they don't want to rewrite that. I dig it. 2) It's fast (except C sometimes) but easier to write than c. Like 100x faster than python. I'm not sure about number two. With the gpu processing revolution wouldn't a python/TensorFlow stack be faster than Fortran? Am I missing something? I remember talking to someone who had worked heavily on at…

[deleted]

Re: Why physicists still use Fortran (2015)

#207

Post by sseagull »

quadruplebond wrote: post #195
sseagull wrote: post #142

Earlier quoted context omitted.

I have been developing in Fortran for years. I just mentioned that as an aside. About C compatiblity: Many C libraries use pointers in their interfaces. Interoperability is indeed defined by the Fortran 2003 standard, which I have used several times to wrap existing C libraries. However, much of the existing code is F90 only (some even F77...), and a vast majority of Fortran developers in the field are not familiar w…

It’s partly the power of library authoring that is moving things I think. To my knowlegdge most post lapack tensor algebra is all C/C++ also. I don’t know Fortran but I am not sure if it has the same flexibility when it comes to generic code and things like writing things like template expression math codes. Finally the fact that groups like Facebook and google are writing their machine learning code in C++ shows tha…

If you don't mind, I'd like to maybe chat with you a bit and get your opinion on some things (and maybe see if I've actually met you before). My (mainly throwaway) email is ytterbium35 (at major email service run by google).

If you don't feel like it, feel free to ignore.

Re: Why physicists still use Fortran (2015)

#208

Post by cowsandmilk »

tyingq wrote: post #48
sbmassey wrote: post #43

Earlier quoted context omitted.

Unless you're passing arrays of pointers to things about, the individual elements in a C array should be contiguous.

>Unless you're passing arrays of pointers That seems to be the context from his example: for(i = 0; i I suppose the counterpoint is that he's doing it wrong. But again, maybe physicists just don't want a tool with that much flexibility.

he's definitely doing it wrong there. As a scientific C programmer, I would never do that, I would malloc one contiguous array of nrows*ncolumns. And my freeing of the array would be as simple as his Fortran deallocate.

Sure, C could make multi-dimensional array handling nicer, but I have macros that basically do his A[x,y,z] for me, admittedly a bit more verbosely.

Many of his points about Fortran are true, but almost all his statements about C are false. Or nearly so, yes, copying an array of floats requires calling a function, memcpy, and not just using an equals sign, but that ain't rough and falls into his idea of "what actually happens ‘under the hood’ inside a computer". And others are easily handled by adopting things like the MKL (want to take the sin of everything in an array, see https://software.intel.com/en-us/mkl-developer-reference-c-t... )

Re: Why physicists still use Fortran (2015)

#209

Post by War_Machine »

cknight wrote: post #162
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…

I worked as a programmer in a molecular dynamics research group for a while. I was asked to work in Python because it was what the boss was familiar with - so there's some of the same inertia happening again, just with a new(er) language, I guess. Speed is not a huge issue if you're happy to leave your simulation running overnight anyway, or if you have the option to just throw more and more cores at the problem (or…

As long as Fortran is able to keep up with Python's capabilities (or any other language's for that matter), there seems to be absolutely no reason to make a change considering Fortran's history and familiarity in Physics. In other words, other languages need to make a big enough leap forward or Fortran to lag behind enough to justify a change. Your example just shows that it's fine to use other languages, and I agree, but it's not very compelling in promoting a change in language.

Re: Why physicists still use Fortran (2015)

#210

Post by shitgoose »

rxhernandez wrote: post #68
thicknavyrain wrote: post #47

Earlier quoted context omitted.

Pretty much just size! There was about 20,000 lines of it, it's legacy code that has been gradually added to since the 1980s, so it would have taken a while to rewrite all the parts to work with each other. Perhaps some day though.

20,000 lines of code really doesn't seem like that much. I probably output that much in about 2-3 months of biomedical research so there has to be more to it than that.

20k of fortran code is a lot. there are no beans/interfaces/adapters/mediators/listeners - just the code that does business.
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