[MITgcm-devel] Re: [MITgcm-support] bug in exch2?

[Martin Losch]

Hi again,
this was meant to go the the devel list in the first place, oh well.

I have tried to find where the nans in the overlaps come from, and  
they appear when u and v are read from the pickup file with  
read_rec_3d_rl.
read_rec_3d_rl calls mdsreadfield, which in turn calls mds_read_fields
In the latter two routines, the array (uVel or vVel) to be read is  
declared as arr(*), but then mds_read_fields calls, eg. mds_seg4torl,  
where the array is declared as
       _RL arr(1-oLx:sNx+oLx,1-oLy:sNy+oLy,nNz,nSx,nSy)
Could that be the source of the problem. I don't know. Should we do  
anything about this?

As a quick fix I can just use the compiler flag, that initilialises  
everything to zero, but that would mask any other problems assciated  
with wrong initializations.

What's your opinion?

Martin
On 11 Jul 2007, at 15:32, Martin Losch wrote:

> Hi there,
>
> there seems to be an initialisation issue in one/some of the exch2  
> routines. On our beloved (God, I hate this machine) SX8, the high- 
> res-cube stops with errors like this:
>>    * 253 Invalid operation PROG=exch2_send_rl2 ELN=1627(40049c9d8)
>>                  Called from read_pickup ELN=2022(40083c6a8)
>>                  Called from ini_fields ELN=1703(4007d9d18)
>>                  Called from initialise_varia ELN=2018(4008154cc)
>> ****  99 Execution suspended PROG=exch2_send_rl2 ELN=1627(40049c9d8)
>>                  Called from exch2_rl2_cube ELN=1966(40048c594)
>>                  Called from exch2_uv_3d_rl ELN=1603(4004a4a74)
>>                  Called from exch_uv_3d_rl ELN=1826(4006f8478)
>>                  Called from read_pickup ELN=2022(40083c6a8)
> so at the first uv exchange. A closer look confirms that array1 and  
> array2 in exch2_send_rl2 have nans on them in the overlap. This  
> problem goes away, when I make the compile initialise everything to  
> zero by default. (I also learned that apparently not the entire  
> overlap is exchanged in exch2_rl2_cube, but only olx-1,oly-1  
> points, at least for cubed exchanges; that would explain, why two  
> exchanges are necessary, wouldn't it?)
>
> Martin
>
>
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