<div dir="ltr"><div><br></div>Dear Marc,<div><br></div><div style>I don't know how much off-track is the following, but give it a check;</div><div style>* compilers may produce code that does different initialization of the IEEE-754 arithmetic (in fact, that are compile time parameters to control exactly that). That can explain at least some part of the divergence.</div>
<div style>In short, even the same compiler can exhibit effects as you describe, with varying tuning; different compilers might have different default ieee754 tuning anyhow.</div><div style><br></div><div style>But there is more to it.</div>
<div style><br></div><div style>You may be hitting one more manifestation of this:</div><div style>* <a href="http://en.wikipedia.org/wiki/Chaos_theory#History">http://en.wikipedia.org/wiki/Chaos_theory#History</a> -> "<span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">An early pioneer of the theory was </span><a href="http://en.wikipedia.org/wiki/Edward_Lorenz" title="Edward Lorenz" class="" style="font-size:13px;text-decoration:none;color:rgb(11,0,128);background-image:none;font-family:sans-serif;line-height:19.1875px">Edward Lorenz</a>...[...]...<span style="color:rgb(0,0,0);font-family:sans-serif;font-size:13px;line-height:19.1875px">had discovered that small changes in initial conditions produced large changes in the long-term outcome</span><span style="color:rgb(0,0,0);font-family:sans-serif;font-size:13px;line-height:19.1875px">"</span></div>
<div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">If you see the errors piling up as time advances, you can pretty much start suspecting this possibility.</span></div><div style>
<span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px"><br></span></div><div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">What do you think, could it be that?</span></div>
<div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px"><br></span></div><div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">best,</span></div>
<div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">F.</span></div><div style><span style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px"><br>
</span></div><div style><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Mar 21, 2014 at 6:30 PM, Marcella, Marc <span dir="ltr"><<a href="mailto:MMarcella@air-worldwide.com" target="_blank">MMarcella@air-worldwide.com</a>></span> wrote:<br>
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<p class="MsoNormal">Hi all,<u></u><u></u></p>
<p class="MsoNormal"><br>
I had a question about wrf and compiler/machine differences that I was hoping to get some clarity on. I am trying to run the same set of wps/wrf compiled executables on two different machines (the libraries for the machine in which the .exe’s were not compiled
on were placed in the exact same location as those on the machine in which the .exe’s were configured/compiled on, hence they run just fine). So essentially, the only difference is the actual machine hardware being used.
<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">For metgrid.exe and real.exe, the results between the two machines are identical, however even with identical met_ems and wrfinput/wrfbdy files, the wrf results are different. By day 58 or so the average differences in TA and especially
precipitation, are quite large (on the order of 1-2mm/day). I am trying to run this over Southeast Asia where there is a lot of cumulus convection. But, I wanted to check if this is to be expected to observe such large differences? I did do a quick internet
and forum search but couldn’t find specific work documenting this. And, I wanted to see if there was a way in the compiling of the code (via a flag, etc that one can add) to get identical results across machines or even compilers? I ask because what is interesting
is that running an identical CCSM.exe on the two machines will yield identical CAM results on the two different machines.
<u></u><u></u></p>
<p class="MsoNormal"><br>
Any help or insight you could lend would be greatly appreciated.<u></u><u></u></p>
<p class="MsoNormal"><br>
Thanks,<br>
Marc<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<br></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr"><span style="font-family:monospace;border-collapse:separate;color:rgb(0,0,0);font-size:medium">-- <br>echo "sysadmin know better bash than english"|sed s/min/mins/ \<br>
| sed 's/better bash/bash better/' # Yelling in a CERN forum<br><br></span></div>
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