A3. I use a PC or PC-based parallel system. Which Fortran 90 compiler should I use?

In our tests the Intel Fortran compiler ifort often generates the fastest executables for x86-based processors (NB, the PathScale Fortran compiler is tied in speed with ifort on AMD processors). The Gnu GCC gfortran compiler is free, widely available and also often very fast. Basically, if you have access to multiple compilers on any given machine, you should just try each one and see what happens.

Here is a sample set of timings on 16 processors of a Cray XK6 system (Jaguar) in December 2011 (MDT). Again – Intel ifort wins, with Gnu gfortran a close second.

examples/crystal/blips/silicon

with the following keywords changed:

vmc_nstep : 800 #*! Number of steps (Integer)
vmc_nconfig_write : 800 #*! Number of configs to write (Integer)
dmc_equil_nstep : 20 #*! Number of steps (Integer)
dmc_stats_nstep : 20 #*! Number of steps (Integer)
dmc_target_weight : 800.d0 #*! Total target weight in DMC (Real)

Total CASINO CPU time DMC energy
Ifort : 54.6394 seconds -63.253019810592 +/- 0.007612017376
Gnu : 62.6400 seconds -63.253019816018 +/- 0.007612049672
Pathscale : 67.8962 seconds -63.259034999613 +/- 0.011000738147
PGF : 72.9000 seconds -63.245897141026 +/- 0.009693089487
Cray : 84.0300 seconds -63.192701255463 +/- 0.006393938977

NB: The pathscale compiler is being deprecated on Crays and is no longer
supported on Jaguar (as of June 2012).

Here is another set of runs for H on graphene (MDT 1.2013) on a Cray XK7 (Titan).

VMC
Gnu 79.65 seconds -282.890716861446 +/- 0.160222570613
PGF 83.74 seconds -282.895599950580 +/- 0.121131726135
Ifort 84.48 seconds -282.970112923443 +/- 0.128262416613
Cray 87.28 seconds -282.890716855184 +/- 0.160222562116
DMC
Gnu 397.20 seconds -284.256578870330 +/- 0.048408651743
Cray 456.63 seconds -284.256578740638 +/- 0.048408642717
Ifort 477.75 seconds -284.252588591933 +/- 0.117686071014
PGF 490.10 seconds -283.915347739145 +/- 0.077180929508

Moral: use the GNU compiler (CASINO_ARCH = linuxpc-gcc-pbs-parallel.titan).

Note: GNU and Cray answers essentially agree with each other, but Ifort (VMC) and PGF (DMC) are giving significantly different answers. This needs to be investigated.

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Category: A: Installing CASINO

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