Re: [ferret_users] arithmetics not working on a variable (broken netCDF file?)

[Steven J Phipps <s.phipps@xxxxxxxxxxx>]

Hi Ryo,

The netCDF file has a few "interesting" features that are confusing 
ferret, as you can see from the warning messages that it generates during 
your session:

 *** NOTE: Ignored modulo length exceeding axis length: lont
 *** NOTE: Ignored modulo length exceeding axis length: lonv
 *** NOTE: Evenly spaced axis has edges definition: dept - ignored

In particular, you are specifying modulo lengths for the axes lont and 
lonv, even though these are only of length one.

You are then trying to shade a 1D region. The variable tdmb has dimensions 
1x100x40x1, so tdmb[k=1,l=1] has dimensions 1x100. When you enter the 
command

shade/k=1/l=1 tdmb

the modulo attribute on the axis lont appears to be confusing ferret into 
thinking that this is really a 2D region, so the shade command succeeds. 
However, when you enter the command

shade/k=1/l=1 tdmb*10

ferret realises that it's a 1D region, and so the shade command fails.

I tried generating a netCDF file that's identical to yours, but without 
the modulo attribute on the axis lont. Now both shade commands fail, as 
they should:

yes? shade/k=1/l=1 tdmb
 **ERROR: dimensions improperly specified: must be a 2D region
          shade/k=1/l=1 tdmb
yes? shade/k=1/l=1 10*tdmb
 **ERROR: dimensions improperly specified: must be a 2D region
          shade/k=1/l=1 10*tdmb

Hope this helps!

Cheers,
Steven

> Hi Ferret users,
>
> I seem to have created a strange netCDF file:
>
>  http://iprc.soest.hawaii.edu/~furue/tmp/tmp.nc
>
> with which you can plot the variable
>
>  shade/k=1/l=1 tdmb
>
> but not if you do some arithmetics with it
>
>  shade/k=1/l=1 tdmb*10
> **ERROR: dimensions improperly specified: must be a 2D region
>          shade/k=1/l=1 tdmb*10
>
> If you define a new variable
>
>  let a = tdmb*10
>
> that can be plotted.  I'm attaching a complete listing below.
>
> There must be something "interesting" about the file,
> but I don't know what it is.
>
> Regards,
> Ryo
> ====================================
> $ ferret
>        NOAA/PMEL TMAP
>        FERRET v6.2
>        Linux(g77) 2.4.21-32 - 05/19/09
>        25-Aug-09 15:49
>
> set mode grat:dash
> set memory/size=400
> Cached data cleared from memory
> keymark 1
> yes? set data tmp.nc
> *** NOTE: Ignored modulo length exceeding axis length: lont
> *** NOTE: Ignored modulo length exceeding axis length: lonv
> *** NOTE: Evenly spaced axis has edges definition: dept - ignored
> yes? show data
>     currently SET data sets:
>    1> ./tmp.nc  (default)
> name     title                             I         J         K         L
> TDMB                                      1:1       1:100     1:40      1:1
>
> yes? shade/k=1/l=1 tdmb
> yes? shade/k=1/l=1 tdmb*10
> **ERROR: dimensions improperly specified: must be a 2D region
>          shade/k=1/l=1 tdmb*10
> yes? let a = tdmb*10
> yes? shade/k=1/l=1 a
> yes?

--
Dr Steven J Phipps

Climate Change Research Centre
Faculty of Science
University of New South Wales
Sydney
NSW 2052
Australia

Tel  +61 2 9385 8957
Fax  +61 2 9385 8969