Fortran Compilers for Use with Source-Code GEMPACK

A suitable Fortran compiler is required for use with all Source-code versions of GEMPACK. For PCs running Windows we support these compilers:

GFortran: This open-source compiler has the advantage of being free, and (in the tests reported at the end of this page) producing the fastest-running EXEs. You must use the particular version that you can download from our site. You'll need GEMPACK Release 11 [Oct 2011] or later.
Intel: Supported since GEMPACK Release 10, this is another fine compiler. We cannot supply the Intel compiler; it must be purchased separately. An Intel Fortran single-user licence can be installed on several PCs used by one person. As an indicative price, in May 2013 an Intel Fortran single-user licence could be purchased for around US$900 (half-price to academics) plus local taxes. See more details here or search through the Intel website (choose Products.....Software.....Compilers to locate the Fortran pages). More GEMPACK-related details here.
Lahey: Since GEMPACK Release 12, the Lahey compiler is not supported. GEMPACK Release 11 supported only the LF95 version of Lahey Fortran [now called LF Express]. Previous GEMPACK Releases supported some earlier versions of Lahey Fortran. LF Express will run under 64-bit Windows, but can produce only 32-bit EXEs. An LF Express single-user licence requires internet activation and can be installed on one PC only. We cannot supply the Lahey compiler; it must be purchased separately. More details here.

Compiler Performance

The different compilers vary both in compile time, and in the run time of the EXE that is produced. Results are quite model-dependent. See the speed comparison table at the bottom of this page. In each case reported there, GFortran runs faster.

I have Intel already -- should I switch to GFortran?

This page explains how you can set up your GEMPACK to use either Intel or GFortran -- so you can experiment to find your own preference.

Purchasing your compiler

Intel sell their Fortran compiler through various resellers. Intel offers academic and multi-user pricing, and is distributed by leading Fortran vendor Polyhedron, or, in Australia, by Devin Trussell of Computer Transition Systems. For GFortran, the free download is here.

32-bit or 64-bit?

Both Intel Fortran and GFortran can be configured to produce either 32-bit or 64-bit EXEs. Most PCs are running a 64-bit version of Windows; 32-bit Windows is fast disappearing. GEMPACK runs well on both. You need to make the choice at GEMPACK install time. Which should you choose ?

A 64-bit EXE will likely run faster, but its main advantage is that it can access more RAM [memory]. So if you think you might want to run a larger model, choose a 64-bit compiler.
A 64-bit EXE will not run on 32-bit Windows. Perhaps that might be a problem if you wanted to distribute your EXE files to others.
A 32-bit EXE runs under 64-bit Windows, but can access less memory.

Usually you should opt for the 64-bit compiler.

Installing your Fortran

Some Releases of GEMPACK only work with specific versions of the Fortran compilers. See these pages for compiler-specific details:

You need to install and test your Fortran before you install source-code GEMPACK. See the above pages for compiler-specific instructions. In each case, we ask that you download, compile, and run a small "Hello World" program to verify your Fortran installation before installing GEMPACK.

Switching back and forth between Fortran versions with GEMPACK

Advanced users who need to do this could study these suggestions.

Non-Windows PCs

A few users run GEMPACK under Linux using the open-source GFortran compiler. See also these notes.

Compiler Performance

The following table, prepared January 2020 using GEMPACK releases 11.3 to 12.1, compares TG-program and GEMSIM run times with 4 large models [GTAP4040, MMRF4, MonUSAoct03 and TERM]. The tests were run a desktop PC running Windows 7 64-bit with a quad-core Intel i7-4770 CPU, 32 GB memory and 512 GB SSD hard drive. Compilers were Intel Fortran 14.0 and GFortran 4.8.1. Times are in seconds. The results reflect in part the various optimization settings used by GEMPACK for different compilers.

recent GEMPACK speedups

Rankings are model-dependent, but for GEMPACK 12.1 GFortran seems to produce faster-running EXEs than Intel (the opposite was true for for GEMPACK 11.3).