[gradsusr] Max Value

[Jeffrey Duda]

Andrew,

I made a script to do the same thing.  I've noticed in mine that I broke up
your one line into two.  That might make the difference.  I think what is
going on is the command is searching through your UNDEF values and finding
those to be the max.  Here's how it goes in my code:

'define mxy = max('ans',x='x1',x='x2')'
'd maxloc(mxy,y='y1',y='y2')'
ymax = subwrd(result,4)

Attached is an image showing how it works.  The field is 850 mb theta-e.
Script output is:

The actual maximum location is at (x,y) = (223,36) or (lat,lon) =
(36.0997,-97.4195) and is 340.864
The actual minimum location is at (x,y) = (146,279) or (lat,lon) =
(42.9153,-100.243) and is 310.718

Before I learned the faster way of doing this, I made another script that
does it using arrays.  It took a bit longer to run, but I never had a
problem with accuracy.  It rejects candidates that are too high or too low.
Here's the beef of that code:

*Finding the location of maximum value
max = -999999
yy = y1
while (yy <= y2)
 'set y 'yy
 'd maxloc('ans',x='x1',x='x2')'
 line = sublin(result,2)
 index = subwrd(line,4)
* if (index < 1e+6 & index > -1e+6)*  (THIS TELLS THE SCRIPT TO REJECT A
POINT IF IT ESSENTIALLY IS OFF THE GRID, I.E., AN UNDEF)
  'set x 'index
  'd 'ans
  line = sublin(result,2)
  act_max = subwrd(line,4)
*setting index of max value into array
  max.yy.1 = index
*setting actual max value into array
  max.yy.2 = act_max
  'set x 'x1' 'x2
  if (max.yy.2 > max)
   max_val = max.yy.2
   max_locx = max.yy.1
   max_locy = yy
   max = max_val
  endif
 endif
 yy = yy + 1
endwhile

Let me know if you have further questions.

Jeff Duda

On Fri, Apr 15, 2011 at 5:53 PM, Andrew Revering <andy at f5data.com> wrote:

>  I’m trying to do a max value plot… I got it to give me coordinates, but
> it’s not quite right. No matter what the variable is on the map that I’m
> trying to find the max value for, it always gives me coordinates (and plots
> visually) in the far lower left corner of the screen where there are no
> values.
>
>
>
> Here is my code:
>
>
>
>
>
> ‘d maxloc(max(tt,x=0,x=1028),y=0,y=768)’
>
> Line=sublin(result,2)
>
> Ygrd=subwrd(line,4)
>
> ‘d maxloc(max(tt,y=0,y=768),x=0,x=1028)’
>
> Line=sublin(result,2)
>
> Xgrd=subwrd(line,4)
>
>
>
> ‘set x ‘xgrd
>
> Lonval = subwrd(result,4)
>
>
>
> ‘set y ‘ygrd
>
> Latval = subwrd(result,4)
>
>
>
> ‘q w2xy ‘lonval’ ‘latval
>
> Xpos = subwrd(result,3)
>
> Ypos = subwrd(result,6)
>
>
>
> Then I go further to plot the coordinate, which works. The printed lat/lon
> is correct for where the marker is, but it is NOT where the max val is. Its
> way down in the lower left corner of the image.
>
>
>
>
>
> _______________________________________________
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>
>


-- 
Jeff Duda
Iowa State University
Meteorology Graduate Student
3134 Agronomy Hall
www.meteor.iastate.edu/~jdduda
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