<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
Dear Users,<br>
just an add up here, although last few mails including MJ's one
completely explains why the values are different. I noted that:<br>
(after all previous define commands as MJ):<br>
<br>
ga-> d a(x=30)<br>
Result value = 1010.57<br>
ga-> d a(x=31)<br>
Result value = 1010.45<br>
ga-> d b(x=29)<br>
Result value = 1010.57<br>
ga-> d c(x=29)<br>
Result value = 1010.57<br>
<br>
ga-> d a(x=1)<br>
Result value = 1011.56<br>
ga-> d a(x=145)<br>
Result value = 1011.56<br>
ga-> d a(x=2)<br>
Result value = 1011.69<br>
ga-> d a(x=146)<br>
Result value = 1011.69<br>
<br>
So, reiterating the previous explanations, x is defined for 146 grid
points (-1.25 to 361.25). Given that somebody does this (although
setting x from 1 to 144 and defining the variable is probably the best
way), aren't the results what to be expected? From my personal point of
view I would like to see that in a bracketed dimension expression
[e.g., a(x=30)], the value of the variable at the 30th grid point of
that variable is extracted instead of the 30th grid point of the
default file. And that's exactly what grads is doing. For that reason,<br>
a(x=31) is same as b(x=30) and so on.<br>
<br>
<br>
regards,<br>
<br>
arindam<br>
<br>
Mary Jo Nath wrote:
<blockquote cite="mid:46716CD6.1040701@noaa.gov" type="cite">
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
<tt>Hi,<br>
<br>
I wasn't able to find anything on the board regarding this issue. Maybe
someone can explain why do I get different values in the script (below)
for the defined variable "a" & "b" ? ("b" and "c" are the same and
correct.) I would expect a = b = c regardless of how I access the
values of those variables. <br>
<br>
Below is the full script and the results. The data file is attached if
anyone would like to run the script on their machine . If you get
different results, please let me know. <br>
<br>
(I'm using Config: v1.9b4 32-bit little-endian on a Linux workstation.
I get the same results, though, using older versions 1.7beta9 and
1.8SL10.)<br>
<br>
I think this is occurring because of this data's grid, where X=1 is
longitude 1.25E instead of 0E. By default GrADS maps "set lon 0 360"
into "X = 0.5 to 144.5", so however "define" works, GrADS returns the
proper value for "a" if "set x 30" is done first, but doesn't return
the expected value if you do<br>
"d a(x=30)". Variables "b" and "c" work because I explicitly "set x 1
144" or "set lon 1.25 358.75" (which correspond to X=1 and X=144 ). <br>
<br>
When I ran a similar script using NCEP data which starts at Lon = 0., I
didn't have this problem.<br>
<br>
Thanks,<br>
Mary Jo<br>
<br>
SCRIPT:<br>
<br>
sdfopen model.slp.nc<br>
set lat 0<br>
q dims<br>
define a=slp<br>
set x 1 144 <br>
q dims<br>
define b=slp<br>
set lon 1.25 358.75<br>
q dims<br>
define c=slp<br>
set x 30<br>
d a<br>
d b<br>
d c<br>
d a(x=30)<br>
d b(x=30)<br>
d c(x=30)<br>
d a-b<br>
d a(x=30)-b(x=30)<br>
d a-c<br>
d a(x=30)-c(x=30)<br>
d b-c<br>
d b(x=30)-c(x=30)<br>
<br>
<br>
RESULTS:<br>
<br>
<b>sdfopen /net2/mjn/model.slp.nc</b><br>
Scanning self-describing file: /net2/mjn/model.slp.nc<br>
SDF file /net2/mjn/model.slp.nc is open as file 1<br>
LON set to 0 360 <br>
LAT set to -89.4944 89.4944 <br>
LEV set to 0 0 <br>
Time values set: 1870:1:16:12 1870:1:16:12 <br>
<b>set lat 0</b><br>
LAT set to 1.01124 1.01124 <br>
<b>q dims</b><br>
Default file number is: 1 <br>
X is varying Lon = 0 to 360 X = 0.5 to 144.5<br>
Y is fixed Lat = 1.01124 Y = 46<br>
Z is fixed Lev = 0 Z = 1<br>
T is fixed Time = 12Z16JAN1870 T = 1<br>
<b>define a=slp</b><br>
Define memory allocation size = 584 bytes<br>
<b>set x 1 144</b> <br>
LON set to 1.25 358.75 <br>
<b>q dims</b><br>
Default file number is: 1 <br>
X is varying Lon = 1.25 to 358.75 X = 1 to 144<br>
Y is fixed Lat = 1.01124 Y = 46<br>
Z is fixed Lev = 0 Z = 1<br>
T is fixed Time = 12Z16JAN1870 T = 1<br>
<b>define b=slp</b><br>
Define memory allocation size = 576 bytes<br>
<b>set lon 1.25 358.75</b><br>
LON set to 1.25 358.75 <br>
<b>q dims</b><br>
Default file number is: 1 <br>
X is varying Lon = 1.25 to 358.75 X = 1 to 144<br>
Y is fixed Lat = 1.01124 Y = 46<br>
Z is fixed Lev = 0 Z = 1<br>
T is fixed Time = 12Z16JAN1870 T = 1<br>
<b>define c=slp</b><br>
Define memory allocation size = 576 bytes<br>
<b>set x 30</b><br>
LON set to 73.75 73.75 <br>
<b>d a</b><br>
Result value = 1010.45 <br>
<b>d b</b><br>
Result value = 1010.45 <br>
<b>d c</b><br>
Result value = 1010.45 <br>
<b>d a(x=30)</b><br>
Result value = 1010.57 <i><==== ????</i><br>
<b>d b(x=30)</b><br>
Result value = 1010.45 <br>
<b>d c(x=30)</b><br>
Result value = 1010.45 <br>
<b>d a-b</b><br>
Result value = 0 <br>
<b>d a(x=30)-b(x=30)</b><br>
Result value = 0.122498 <i><==== a != b</i><br>
<b>d a-c</b><br>
<b>Result value = 0 <br>
d a(x=30)-c(x=30)</b><br>
Result value = 0.122498 <i><=== a != c</i><br>
<b>d b-c</b><br>
Result value = 0 <br>
<b>d b(x=30)-c(x=30</b>)<br>
Result value = 0 <br>
EOF EXECuting test_script<br>
</tt>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
----------------------------
ARINDAM CHAKRABORTY
Department of Meteorology
Florida State University
Tallahassee, FL-32306, USA
Tel: +001-850-6443524 (Off)
+001-850-5758550 (Res)
Fax: +001-850-6449642
____________________________
</pre>
</body>
</html>