[MITgcm-support] How to calculate the RAM requirement?

[Göran Broström]

Yes I mean 8 byte, sorry about that.

Good information!!
I never actually tested the formula but it has worked fine as a rule of thumb 
for my applications. Good job.

Göran



 when your model barely fit into the memory
> Göran Broström wrote:
>> Hi all,  
>>  
>> To contribute to the confusion :) A long time ago I got a formula (from 
Chris) 
>> size=nx*ny*nz*8*50 
>> (grid points * 8 bits * 50 fields) 
>> That would make about 10 GB. Perhaps it should be 100 fields in the new 
model 
>> and with ice as suggested by Dimitris.
> Do you mean 8 bytes?
>
> A few months ago I measured the working set size of a simple 3D 
> hydrodynamics-only run on 1 CPU and compared it with the size of a 3D 
> double-precision array (nx*ny*nz*8 bytes). The ratio (let's call it R) 
> varied between 34 and 71. The main determining factors were:
>
>     * The timeave package is quite expensive, as you'd expect,
>       increasing R by about 20.
>     * Using a 2 subgrids in each direction (nSx = nSy = 2) reduces R by
>       about 8-10 relative to a single-subgrid run. But this trend
>       reverses when nSx or nSy is increased beyond about 2.
>
> -- 
> Mark Hadfield          "Ka puwaha te tai nei, Hoea tahi tatou"
> m.hadfield at niwa.co.nz
> National Institute for Water and Atmospheric Research (NIWA)
>
>
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