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 Intel and Lahey compilers:

Intel: Supported since GEMPACK Release 10, this is probably the best performing compiler. It can produce 32-bit or 64-bit EXEs. We cannot supply the Intel compiler; it must be purchased separately. An Intel Fortran single-user licence does not require internet activation and can be installed on several PCs used by one person. As an indicative price, in July 2010 an Intel Fortran single-user licence could be purchased for US$699 (academic:US$280) plus local taxes. See more details here or search through the Intel website (choose Products.....Software.....Compilers to locate the Fortran pages). More details here.
Lahey: Since GEMPACK Release 11, only the LF95 version of Lahey Fortran [now called LF Express] is supported. Previous GEMPACK Releases supported some earlier versions of Lahey Fortran. Lahey Fortran 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.

For GEMPACK Release 11 [Oct 2011] we will also support:

GFortran: This open-source compiler has the advantage of being free. It can produce 32-bit or 64-bit EXEs. You must use the particular version that you download from our site. More details here.

Purchasing your compiler

Intel sell their Fortran compiler through various resellers and Lahey also sell through distributors and dealers. Both Lahey and Intel offer academic and multi-user pricing, and both are distributed by leading Fortran vendor Polyhedron, or, in Australia, by Devin Trussell of Computer Transition Systems.

32-bit or 64-bit?

More and more PCs are running a 64-bit version of Windows, although 32-bit Windows is still widely used. GEMPACK runs well on both. Both Intel Fortran and GFortran can be configured to produce either 32-bit or 64-bit EXEs. Which should you choose ?

The only advantage of a 64-bit EXE is that it can access more RAM [memory]. So if you are in the small group who wishes to run a really huge model (on 64-bit Windows), choose a 64-bit compiler.
A 64-bit EXE will not run on 32-bit Windows. That could be a problem if you wanted to distribute your EXE files to others.
A 32-bit EXE runs fine under 64-bit Windows.

See also this GEMPACK-oriented comparison of 32-bit and 64-bit Windows.

Installing your Fortran

You need to install and test your Fortran before you install source-code GEMPACK. See these 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.

Match Fortran version to GEMPACK Release

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

Intel
Lahey

Switching back and forth between Fortran versions with GEMPACK

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

Non-Windows PCs

A Fortran compiler usually comes with Unix, or is an optional extra. A few users have compiled GEMPACK under Linux using the open-source GFortran compiler. See also these notes.

Compiler Performance

The following table, prepared October 2011 using GEMPACK release 11, compares run (and LTG=compile) time with 4 large models. All tests were run on 64-bit Vista using an Intel Core 2 Quad CPU. The results reflect in part the various optimization settings used by GEMPACK for different compilers. In particular the GEMPACK team has spent more effort tuning compiler settings for Intel Fortran. Comparison of of Fortrans performance

Results are model-dependent, but in general Intel runs twice as fast as LF95 or GFortran (which take similar times). However, LF95 is much the quickest at the LTG (compile) stage.