[MITgcm-support] ifort optimization puzzle

[Martin Losch]

Patrick,

I can turn off mnc in data.pkg (useMNC=.FALSE.) and get the same 
(wrong) results.
When I turn off mnc in packages.conf, I still get the same (wrong) 
results.

So MNC is off the hook (o:

Martin

On Mar 8, 2005, at 10:46 AM, Patrick Heimbach wrote:

>
> Hi Martin,
>
> a potentially similar problem was reported (off list)
> by a user from Norway. He identified problems when using
> optimization with ifort in conjunction with the mnc package.
> To confirm, could you try using same setup without mnc,
> and see whether problems persist?
> (I will try to get more details).
>
> -Patrick
>
>
>
> Quoting Martin Losch <mlosch at awi-bremerhaven.de>:
>
>> Hi,
>>
>> together with Michael Schodlok I have set up a 1D experiment: 1 column
>> of water (nx=ny=1, overlap=2, nr=30, dz=30*10). We specify zero net
>> surface heat flux (qnet = 0), but -50W/m^2 shortwave heat flux 
>> (warming
>> due to the sun), in order to drive kpp. This works all very nicely and
>> we were happy, the mean temperature was constant, as it should (why
>> didn't we stop there?). Then I suggested to move to a faster machine
>> (from a $%^&* SUN to a nice linux-box with ifort). We used the 
>> standard
>> ifort build-options file with paths to netcdf appended. But suddenly
>> the system was losing heat at 1200W/m^2. Turning off optimization 
>> (-O0)
>> or using g77 gave the old results (with constant mean temperature). We
>> clearly have an optimization problem here. How serious do you think
>> this is (I admit that we are using a somewhat pathological
>> configuration)?
>>
>> Martin
>>
>> PS. in sea.mit.edu:/data4/mlosch/test1d.tgz I have a case similar to
>> our original one, but with different initial conditions for T and S,
>> here the mean temperature decreases by 0.5degC in 10 days,
>> corresponding to approximately 690W/m^2 heat loss
>> build_g77 has the Makefile for g77 (result in run00/mnc_0001)
>> build_o0 for ifort -O0 (result in run00/mnc_0002)
>> build_o1 for ifort -O1 (gives almost the same results as -O3, result 
>> in
>> run00/mnc_0003)
>> data files etc. in run00
>> I included the build option files I used, but I manipulated the
>> makefiles afterwards to change the optimization level for ifort.
>>
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>>
>
>
> --------------------------------------------------------
> Patrick Heimbach   Massachusetts Institute of Technology
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>