Re: NCL 5.1.1: Issues with concatenating a subset of an array from multiple files

Hi Yongxin,

There were some fairly serious bugs in the addfiles implementation in
NCL 5.1.0, most of which were fixed for 5.1.1. A problem that remained
in 5.1.1 involved vector subscripting along the aggregated dimension.
Since you are not using vector subscripting that would not affect you.

However, your statements concerning the behavior of addfiles suggest
to me that you are expecting addfiles to behave as it did prior to NCL
5.1.0. We considered that behavior a bug and spent considerable energy
fixing it.

Given your situation of 2 files with a variable RAIN that is
dimensioned 25, 765, 1191 and the following statement:

obs_rain = rain_fin[:]->RAIN(0:23,:,:)

the resulting dimensionality should be 24,765,1191. In other words,
the left-most dimension is implicitly aggregated into a dimension of
50 elements (assuming 'cat' mode). You are just picking the first 24
of them. It is true that prior to 5.1.0 the behavior of this statement
was different: it would have picked the first 24 elements of each file
aggregated. But based on much user input we decided that that behavior
was incorrect: it was inconsistent with the normal behavior of NCL's
array subscripting syntax and it made it difficult in particular to
work with files where the number of elements along the aggregated
dimension varies. I hope this is clear and you can appreciate why the
change was made. Anyway I think NCL is working as currently documented
for you.
  -dave

On Sep 22, 2010, at 10:53 AM, Yongxin Zhang wrote:

> Hi Dennis,
>
> Thanks for your email. I am wondering if you have tried v5.2.1
> with reading out and then concatenating a subset of the array (say 3
> time steps from the first WRF file and 4 time steps from the second
> WRF file) since that is where v5.1.0 and v5.1.1 have some issues.
>
> Yongxin
>
> On Wed, Sep 22, 2010 at 10:44 AM, Dennis Shea <shea@ucar.edu> wrote:
> v5.1.0 was released in March 2009
> v5.1.1 was released in June 2009
>
> http://www.ncl.ucar.edu/prev_releases.shtml#AddfilesBugsFixed5.1.1
>
> =================================
> The current version is v5.2.1
> It may be downloaded from: http://www.ncl.ucar.edu/Download/
>
> It works correctly on the following simple test.
> =================================
>
> I tried v5.2.1 with 2 WRF files. One had 5 time steps;
> the other had 6 time steps
>
> ===> file 1
> netcdf wrf-00-09.sample_t0-4 {
> dimensions:
> Time = UNLIMITED ; // (5 currently)
> [snip]
> variables:
> float PH(Time, bottom_top_stag, south_north, west_east) ;
>
> ===> file 2
> netcdf wrf-00-09.sample_t5-10 {
> dimensions:
> Time = UNLIMITED ; // (6 currently)
> [snip]
> variables:
> float PH(Time, bottom_top_stag, south_north, west_east) ;
> [snip]
>
> +++++++++
>
>
> fils = systemfunc("ls wrf-00-09*nc")
> ph= f[:]->PH
> printVarSummary(ph)
>
>
> Variable: ph
> Type: float
> Total Size: 90700632 bytes
> 22675158 values
> Number of Dimensions: 4
> Dimensions and sizes: [Time | 11] x [bottom_top_stag | 58] x
> [south_north | 99] x [west_east | 359]
> Coordinates:
> Number Of Attributes: 6
> FieldType : 104
> MemoryOrder : XYZ
> description : perturbation geopotential
> units : m2 s-2
> stagger : Z
> coordinates : XLONG XLAT
>
>
>
> On 09/22/2010 09:22 AM, Yongxin Zhang wrote:
> I have two netCDF files that contain only one variable, RAIN. RAIN is
> dimensioned as (time, south_north, west_east) where time=25,
> south_north=765 and west_east=1191. I needed to read out the first 24
> data (i.e., time=0 to 23) at each grid point from each file and then
> concatenate them to become a new variable. I used "systemfunc" and
> "addfiles" but strange thing was that when I used the following
> statement
>
> obs_rain = rain_fin[:]->RAIN(0:23,:,:)
>
> I would get obs_rain dimensioned as (24, 765, 1191) instead of (48,
> 765,
> 1191). Same thing happened even though I explicitly set
> ListSetType(rain_fin,"cat"). However, if I used this statement
>
> obs_rain00 = rain_fin[:]->RAIN(:,:,:)
>
> I would get obs_rain00 dimensioned as (50, 765, 1191) which is
> right. I
> tried this on two different Linux clusters at NCAR using both NCL
> 5.1.1
> and NCL 5.1.0 and I got the same results. I am not sure if there is a
> bug in NCL 5.1.1 and NCL 5.1.0 or I need to set something else. Please
> advise. Thanks.
>
> Yongxin
>
>
>
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>
> --
> ======================================================
> Dennis J. Shea tel: 303-497-1361 |
> P.O. Box 3000 fax: 303-497-1333 |
> Climate Analysis Section |
> Climate & Global Dynamics Div. |
> National Center for Atmospheric Research |
> Boulder, CO 80307 |
> USA email: shea 'at' ucar.edu |
> ======================================================
>
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Received on Wed Sep 22 12:05:27 2010