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Hi Everyone,<br>
<br>
I'm confused and have a question... how does what Arindam sent below
differ from the GrADS "tregr" function?<br>
<a class="moz-txt-link-freetext" href="http://grads.iges.org/grads/gadoc/gradfunctregr.html">http://grads.iges.org/grads/gadoc/gradfunctregr.html</a><br>
<br>
Thanks for all your help in advance,<br>
Chuck<br>
<br>
Arindam Chakraborty wrote:
<blockquote
cite="midPine.LNX.4.44.0506251735001.15242-100000@io.met.fsu.edu"
type="cite">
<pre wrap="">hi Shailendra,
to plot a linear trend, you need to compute the slop and
y-intercept of the time series. A least square fit can be done
to obtain those two parameters. Here is an example to calculate
those and plot the linear trend.
'open file'
'set lon 88'
'set lat 0'
'set t 1 24' * assuming this is the time limit
'define yvar = aave(...)'
'd yvar'
* make a variable 1, 2, ..., 24 to calculate m and c of y = mx + c
'xvar = yvar*0 + 1'
'xvar = const(xvar,1,-u)'
'xvar = 25 - sum(xvar,t+0,t=24)'
'set t 1'
'define p = sum(xvar,t=1,t=24)'
'define q = sum(yvar,t=1,t=24)'
'define r = sum(xvar*yvar,t=1,t=24)'
'define s = sum(xvar*xvar,t=1,t=24)'
'define rn = ave(xvar*yvar,t=1,t=24)'
'define n = r/rn'
'define amp = (n*r - p*q)/(n*s - p*p)' * this is m
'define ave = (q - amp*p)/n' * this is c
'set t 1 24'
'd amp*xvar + ave'
Hope this helps,
----------------------------
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
____________________________
On Sat, 25 Jun 2005, Shailendra Rai wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hello,
</pre>
</blockquote>
<pre wrap=""><!---->I have plotted a time series of area averaged variable variable with time. Is their any way in gradsc to plot the trend as a straight line ???
With regards
Shailendra Rai
K. Banerjee Centre of Atmospheric and Ocean Studies
University of Allahabad
Allahabad
INDIA
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
********************************************************************
Charles Seman <a class="moz-txt-link-abbreviated" href="mailto:charles.seman@noaa.gov">charles.seman@noaa.gov</a>
U.S. Department of Commerce / NOAA / OAR
Geophysical Fluid Dynamics Laboratory voice: (609) 452-6547
201 Forrestal Road fax: (609) 987-5063
Princeton, NJ 08540-6649 <a class="moz-txt-link-freetext" href="http://www.gfdl.noaa.gov/~cjs/">http://www.gfdl.noaa.gov/~cjs/</a>
********************************************************************
"The contents of this message are mine personally and do not reflect
any position of the Government or NOAA."
</pre>
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