[ncl-talk] Suspected bug in calculate_daily_values

[Adam Phillips]

Hi Dave,
Thanks for reporting this and for investigating the root cause. I have
filed a JIRA ticket: NCL-2656.
Thanks again,
Adam


On Tue, Sep 12, 2017 at 7:43 AM, Dave Macleod <
David.Macleod at physics.ox.ac.uk> wrote:

> Hi,
>
> Long time user, first time emailer ... thanks for all the hard work on
> NCL! FYI, I believe I have found a bug in calculate_daily_values.
>
> The argument "nDim" is meant to identify the time dimension, but in fact
> the function only works correctly when nDim=0 (in the case of
> 2,3,4-dimensional data), and nDim=1 (in the case of 5D data).
>
> I have copied a MWE below to demonstrate. But I have traced the problem to
> point of the statistical operation in the function (e.g. line 18402 in
> /contributed.ncl, NCL v 6.4.0):
>
> > xStat(:,nt,:,:,:)  = dim_avg_n( x(:,it,:,:,:), nDim)
>
> Here "nDim" specifies the dimension on which to carry out the averaging
> and "it" is the index corresponding to day "nt" . Since "it" is hard-coded
> on dimension #1, any value of nDim not equal to 1 will not produce the
> correct result.
>
> Similarly for the 2,3,4D case,
> > xStat(nt,:,:,:)  = dim_avg_n( x(it,:,:,:), nDim)
>
> ...requires nDim=0.
>
> A quick fix would be to modify the 5D case such that it require nDim=0,
> then add a error condition that nDim=0. Or something more clever to
> preserve the functionality of nDim! (I think there is also an issue where
> the xStat is defined according to dimx).
>
> NB, from the code I think the same error may affect
> calculate_monthly_values and possibly calculate_segment_values, though I
> haven't tested this.
>
> All the best,
> Dave MacLeod
> -------------------------------------
> Postdoctoral Research Scientist
> Atmospheric Oceanic and Planetary Physics, University of Oxford
>
>
> MWE demonstrating the problem described above:
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
> begin
>
> ; 2D, 3D, 4D data: only works if nDim=0
> x4D=random_uniform(-1.0,1.0,(/4,4,4,4/))        ; dummy data
> nDim=0                                          ; choose a dimension to
> be 'time' - CHANGE FROM A VALUE DIFFERENT FROM ZERO TO BREAK
> x4D!nDim="time"                         ; add metadata; 4 points, over 2
> days
> x4D&time=fspan(0.25,1.75,4)
> x4D&time at units="days since 2017-09-12"
> printVarSummary(x4D)
> x4DDay = calculate_daily_values (x4D, "avg",nDim, False)
> printVarSummary(x4DDay)
>
>
> ; 5D data: only works if nDim=1
> x5D=random_uniform(-1.0,1.0,(/4,4,4,4,4/))      ; dummy data
> nDim=1                                          ; choose a dimension to
> be 'time' - CHANGE TO A VALUE DIFFERENT FROM ONE TO BREAK
> x5D!nDim="time"                         ; add metadata; 4 points, over 2
> days
> x5D&time=fspan(0.25,1.75,4)
> x5D&time at units="days since 2017-09-12"
> printVarSummary(x5D)
> x5DDay = calculate_daily_values (x5D, "avg",nDim, False)
> printVarSummary(x5DDay)
> end
>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>
>


-- 
Adam Phillips
Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
www.cgd.ucar.edu/staff/asphilli/   303-497-1726

<http://www.cgd.ucar.edu/staff/asphilli>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.ucar.edu/pipermail/ncl-talk/attachments/20170912/47d94616/attachment.html>