id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
301	xlf95 difference from ifort12 (et al) on IT-PP-05	Ian Culverwell	Ian Culverwell	"Following the replacement of the OCC-derived ropp_pp reference files with those from ROPP6.0, a discrepancy has come to light between the results of IT-PP-05 when ROPP is compiled with xlf95 (running under AIX on an IBM supercomputer) and when it is compiled with ifort12 ''and all the other compilers'' running on a linux box.

Investigations show that this discrepancy has been there as long as we have been testing xlf95, but that previously it was masked by the much larger difference between ROPP (built with any compiler) and OCC. 

IT-PP-05 tests the ropp_pp_occ_tool on open and closed loop GRAS data. The figure below shows the differences between xlf95 and ifort, and between ROPP6.0 and 6.1, on the third profile of the test dataset, where the differences are largest. 

[[Image(test2_bangle.gif)]]

It is clear that the difference in bangle between xlf95 and ifort12 is pretty much the same at 6.1 as it was 6.0, because the 6.0-to-6.1 change is very small.  (Offline tests indicate that this small difference is largely due to a change in ropp_pp_fourier_filter.f90 made at 6.1 (see #299).) 

The same is true for refractivity. 

[[Image(test2_refrac.gif)]]

Painstaking investigations have yet to discover the reason for the difference between xlf95 and ifort12 (etc) on this dataset.  It may be down to a deep-rooted difference in the performance of fortran intrinsics on the two compilers/platforms. We propose ""parking"" the issue for the moment, as it is delaying the release of ROPP6.1.
"	defect	closed	normal	7.0	ropp_pp	6.0	fixed