Opening multiple files, lats4d "stats" option

[Arlindo da Silva]

On 9/25/07, Jason Snyder <jmssnyder at ucdavis.edu> wrote:
>
> I am trying to open two files in GRADS with different time indices.  How
> can
> I go about doing this.  I want to subtract the values in one file from the
> values in the other file.  I have tried opening the files with XDFOPEN but
> it does not work.  I am using GRADS 1.7.  Is there a more advanced GRADS
> that can allow me to do this?


You can either type or you can lie. The verbose way requires that you be
explicit about the "t" levels you are operating on:

sdfopen file1.nc
sdfopen file2.nc
display var.1(t=1) - var.2(t=1)

Or you can lie to GrADS: just create a file2.ddf where you specify the TDEF
keyword to force the same time axis as file 1; see the xdfopen documentation
for info on creating DDF's. If you use a recent version of lats4d supporting
the "-j" option you should be able to create a difference file like this:

lats4d -v -i file.nc -j file2.ddf -o diff -func '@.1- at .2'

This will create file "diff.nc" with the difference of the two. BTW, if you
want to have a simple summary of the difference between the 2 files
(min/max/ave) just use "stats" for format:

lats4d -v -i file.nc -j file2.ddf -format stats -func '@.1- at .2'

This gives you a quick way to compare 2 structurally identical files. Or you
can use "stats" on a single file, e.g.,

lats4d -i model -format stats

The output is something like this:

<stats>
+
+ <> Statistics on 00Z01JAN1987 for "model"
+
+    Name    Lev         Min         Max        MEAN        STDV         RMS
+ --------- ---- ----------- ----------- ----------- ----------- -----------
+ ps         sfc    481.9110   1049.9100    953.2780    102.9510    958.8190
+ ts         sfc    230.9930    318.4930    278.5030     18.7761    279.1350
+ pr         sfc      0.0000  0.00087738  3.1217e-05  5.9594e-05  6.7267e-05

     Name    Lev         Min         Max        MEAN        STDV         RMS
  --------- ---- ----------- ----------- ----------- ----------- -----------
  ua        1000    -12.9719     20.0281     -0.5000      6.5431      6.5601
  ua         850    -22.5107     29.7393      1.6346      8.3796      8.5361
  ua         700    -19.0453     33.9547      3.8051      9.2721     10.0211
  ua         500    -26.0697     50.9303      6.8472     11.9436     13.7655
  ua         300    -30.2449     73.7551     12.3417     16.0525     20.2465
  ua         200    -18.9862     81.0138     14.3253     16.6570     21.9678
  ua         100    -19.2900     53.7100     11.3790     12.8742     17.1807
  --------- ---- ----------- ----------- ----------- ----------- -----------
+ ua           7    -30.2449     81.0138      7.1190     11.9897     15.0878

[snip]

You can pipe the output through "grep '^+'" to omit the vertical level
details. This feature was added with the "-j" option.

  Good Luck,

       Arlindo





--
Arlindo da Silva
dasilva at alum.mit.edu
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