What can Fortran do with multidimensional arrays that C can’t ?

Three things I can think of off the top of my head:

ALLOCATE(foo(imax,jmax,kmax))

a=b+c # where a, b, and c are arrays of the same dimensionality and size

a=MATMUL(b,x)+c

These are all things built into the Fortran 90 language, BTW. Admittedly most of these are just conveniences, but being able to to do multidimensional array operations without having to think too hard about “Did I vectorize that correctly?” is a big win IMHO.

I’ve worked in user support at a supercomputer center for a little over 8 years, and IMHO many scientists who switch from Fortran to C probably shouldn’t. There’s an old saw about how a good Fortran programmer is able to write Fortran in any language; unfortunately, this also holds true for virtually all naive and/or bad Fortran programmers as well, and C isn’t nearly as forgiving as Fortran. Working with multidimensional arrays in C can be actively painful, and the ways to shoot yourself in the foot with malloc() are many and varied.

A humorous anecdote about C++ vs. Fortran: One user I worked with had a huge molecular dynamics program that he’d written in C++… but the routine that was the innermost loop of the calculation, the one where most of the time was spent, was written in Fortran. I once asked him why he didn’t implement that routine in C++ too, because he went to heroic efforts to link this one Fortran routine with his C++ app. His response was something to the effect of “I tried that once, and the code slowed down by a factor of two.”

http://www.canada.com/national/nationalpost/news/cnspolitics/story.html?id=a320fffa-9ff7-48b6-b975-86cdef0b4228

Here is the start of the article:

Medical researchers caught faking it
Federal grant recipients

Margaret Munro, CanWest News Service
Published: Thursday, March 16, 2006
More than a dozen scientists and doctors, several of them recipients of sizable federal grants, have been faking research, destroying data, plagiarizing or conducting experiments on people without necessary ethics approvals, the country’s lead research agencies report.

One medical researcher, who was awarded $1,347,445 for various projects, fabricated and falsified data and was permanently barred last year from receiving more federal money, according to documents obtained by CanWest News Service.

Check out the April 7th cartoon. It’s like deja’vu all over again

True, with big caveats. As I was pointing out, my friend operates supercomputers (and clusters), and the run time of software is typically on the order of days or weeks, during which time it might hog hundreds of nodes and/or some big machines. There’s often a queue of programs waiting to run. So, performance can be an issue

As you point out, climate models can be of even greater magnitude. There can be whole cluster or clusters dedicated to a single model for long run periods. Additionally, the models are not all that mathematically complex (as I understand it), rather deal with a large grid of data. I suspect in that circumstance C will be best, as it’s good for light things with many repetitions. Of course, some of my assumptions about how the modeling works could be wrong.