[gradsusr] difference between field and single point values for the same defined expression

[Helio Camargo]

Thanks for the reply, Jeff!

That was my guess as well. I thought it was just strange the fact that
Grads truncates when plotting te field but doesn´t do it when setting a
single point...

Regards,


--
Helio

On Sat, Apr 30, 2016 at 4:52 PM, Jeff Duda <jeffduda319 at gmail.com> wrote:

> My only guess is that since the differences are so small, Grads just
> truncates them to zero.
>
> Jeff Duda
>
> On Fri, Apr 29, 2016 at 2:36 PM, Helio Camargo <heliocamargo at gmail.com>
> wrote:
>
>>
>> I´m performing the following expressions over time 1 of a 50 ensemble
>> member run:
>>
>> 'set t 1 last'
>> 'set e 1 last'
>> 'define ens = tpratesfc.1 '
>>
>> 1) 'define smens = sum(ens,e=1,e=50)'
>> 2) 'define 'smensmsk =  maskout(sum(ens,e=1,e=50),sum(ens,e=1,e=50)-0)'
>> 3) 'define 'smensmskcnst
>> = const(maskout(sum(ens,e=1,e=50),sum(ens,e=1,e=50)-0),0,-u)'
>>
>> 'set t 1'
>>
>> For some reason, for t=1, expression 1, yelds small negative values
>> (smens.gif, attached). Expressions 2 and 3 should set undef to these
>> negative values and set 0 for these undef grid points respectively. Looking
>> at the figures smensmsk.gif and smensmskcnst.gif, these operations seem to
>> work perfectly
>>
>> And setting lon/lat to a point where the above operations should
>> influence, is consistent with the figures above:
>> Lon = 298.442  Lat = -28.8304
>>
>> *ga-> d smens*
>> *Result value = -8.33652e-19*
>>
>> *ga-> d smensmsk*
>> *Result value = -9.99e+08*
>>
>> *ga-> d smensmskcnst*
>> *Result value = 0*
>>
>> ** differences also show expected result*
>> *> operation 2 - operation 1*
>> ga-> d smensmsk-smens
>> Result value = -9.99e+08
>>
>> *> operation 3 - operation 2*
>> ga-> d smensmskcnst-smensmsk
>> Result value = -9.99e+08
>>
>> *> operation 3 - operation 1*
>> ga-> d smensmskcnst-ens
>> Result value = 1.9073e-20
>>
>> However, making FIELD  diferences between defined expression 3 and
>> defined expression 1 results "Constant Field=0"
>> (diff_smensmskcnstsmens.gif).
>>
>> Can anyone explain why this is happening?
>>
>> Thanks in advance for your patience.
>> --
>> Helio
>>
>> _______________________________________________
>> gradsusr mailing list
>> gradsusr at gradsusr.org
>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
>>
>
>
> --
> Jeff Duda
> Graduate research assistant
> University of Oklahoma School of Meteorology
> Center for Analysis and Prediction of Storms
>
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20160506/8a81bf26/attachment.html