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Why physicists still use Fortran (2015)

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Re: Why physicists still use Fortran (2015)

#61

Post by pbhjpbhj »

thicknavyrain wrote: post #47
serf wrote: post #39

Earlier quoted context omitted.

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…

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.

What's the code do? [physics grad level description would be fine]

It must surely be generic equipment management, you're not running experiments in physics that are > 30 years old, surely?

Re: Why physicists still use Fortran (2015)

#62

Post by ChuckMcM »

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…

Now you need to do a follow on study to see how much science the 'rival' group does with a more modern codebase than your 'legacy' group does. Would you know if there are enough examples of two groups who have diverged like this to get meaningful (as in statistically significant) results on the cost benefit of porting / not porting?

Re: Why physicists still use Fortran (2015)

#63

Post by eesmith »

coliveira wrote: post #32
quickben wrote: post #19

Earlier quoted context omitted.

"Fortran is faster than C++" Whats your usecase? It seems it is faster for some, but a lot slower in others: https://benchmarksgame.alioth.debian.org/u64q/compare.php?la...

When people say that FORTRAN is faster than C++ it is obviously for numerical code, since general systems code is very hard to do in FORTRAN. Many people will complain that C++ can be faster than FORTRAN, however the problem is that you need to know a lot of C++ or have access to the right libraries to write competitive numeric code. In FORTRAN you can do that out of the box.

Moreover, the article mentions this point, references the benchmarks game, and says "However, the two benchmarks where Fortran wins (n-body simulation and calculation of spectra) are the most physics-y".

Re: Why physicists still use Fortran (2015)

#64

Post by sbmassey »

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.

Fair enough then, I suppose that in C you have to do something like that if you want both that your matrix size is decidable at runtime, and to be able to index it with m[x][y] rather than some function.

Re: Why physicists still use Fortran (2015)

#65

Post by cm2187 »

ryl00 wrote: post #60
cm2187 wrote: post #35

Earlier quoted context omitted.

I needed a .net math library. My IT department insisted on my trying a wrapper around a Fortran library (I believe purely because they had a license already). All the classes and variables names are short hexadecimals strings. None of the interface is idiomatic to .net (the library only has void returning methods which pass error codes as byref arguments instead of using exceptions, requesting a parameter for the len…

Sounds like your IT department botched the wrapper. Wouldn't a more successful candidate likely just have used an abstraction layer between the .net conventions you were expecting and whatever the native code was doing?

Nope, the library itself is sold that way. See the documentation:

https://www.nag.co.uk/numeric/DT/nagdotnet_dtw02/html/conten...

Re: Why physicists still use Fortran (2015)

#66

Post by walshemj »

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 recall that a local aerospace outfit was looking for C++ programmers to re do a metric F%^K ton of Fortran into c++.

I actually rang the recruiter to query why would not be simpler to train your existing staff to use Fortran - the add stayed up for years and years I always wonder if it ever got ported.

Re: Why physicists still use Fortran (2015)

#67

Post by walshemj »

thicknavyrain wrote: post #47
serf wrote: post #39

Earlier quoted context omitted.

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…

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.

Only 20k I have worked on bigger Fortran systems doing billing systems for a telco oddly enough.

Re: Why physicists still use Fortran (2015)

#68

Post by rxhernandez »

thicknavyrain wrote: post #47
serf wrote: post #39

Earlier quoted context omitted.

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…

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.

Re: Why physicists still use Fortran (2015)

#69

Post by vram22 »

nejenendn wrote: post #25
dahart wrote: post #5

> Interestingly, C/C++ beats Fortran on all but two of the benchmarks, although they are fairly close on most. I think this is fairly recent that C/C++ wins. I don’t know how recent exactly, but I remember a colloquium not too long ago by a compiler researcher who said that cross-compiling to Fortran and then optimizing almost always produced faster code than the C/C++ compiler could. Fortran is apparently easier to…

Fortran is easier to optimize compared to c/++ if you don’t use restrict for the c end. If you do use restrict (iirc) the compilers are competitive.

It say something like that here:

https://en.wikipedia.org/wiki/Restrict

Re: Why physicists still use Fortran (2015)

#70

Post by cubano »

I have a somewhat amusing FORTRAN story from my undergrad days at the Florida Institute of Technology...

So my first programming class ever was a Numerical Analysis class taught at FIT, and to be honest, this was my first exposure to a "real" editor (vi on a PDP11 in this case)..up to then it was all MS-BASIC with that wonky line editor and, of course, goto-s and line numbers.

At the end of the first class (8am ugh), the instructor announced that anyone looking to get extra credit and perhaps skip having to come to early class, to talk to him after class. Of course that sounded good to me, so I went to see him and he said "ok...if you can write me a bowling league manager in 10 weeks you will get an A and not have to ever come to class."

Ok...hell yes in fact! This sounded a ton more interesting then sitting around a silly class talking about programming. He gave me a spec sheet and away I went to lab to begin my struggles with vi and FORTRAN.

I wasn't easy, but holy shit did i learn a lot...more then I ever could have just doing the exercises in floating-point rounding error and non-linear simulations (I ended up doing that later as well) that were "taught" in class.

I can still remember FORTRAN (77 I believe) has the a very strict formatting scheme where the column had to match the keyword in order of the program to compile or something stringent like that. But mostly, coming from BASIC, it was a breath of fresh air.

I ended with completing the program with extra bells and whistles...sorting, multiple leagues and other things...and the instructor was duly impressed.

I got my A and never woke up before 8am again.

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