Re: summation problem

[Paul van Delst <paul.vandelst(at)noaa.gov>]

Jaco van Gorkom wrote:
> 
> Manish wrote:
>  ...
> > I have a program which produces an array of values of sunlight flux during
> > the day.  Unfortunately, it produces crazy numbers before the sunrises and
> > after it sets(as expected).  I'm summing the values throughout the day to
> > get a total integrated day flux, but here's the problem - is there a way of
> > telling the TOTAL function to ignore negative numbers and NaN numbers?
> 
> Yes, there is a way:
> IDL> test = [0,-1,3,4,]
> IDL> print, total(test>0,/nan)
>       7.00000
> % Program caused arithmetic error: Floating illegal operand
> 
> The 'illegal operand' error appears to be harmless, caused by comparing test>0:
> IDL> print, test>0
>       0.00000      0.00000      3.00000      4.00000          NaN
> % Program caused arithmetic error: Floating illegal operand

Harmless maybe, but I for one don't like seeing illegal operand errors, let alone ignoring
them. What if you add some code that tries to take the log of a -ve number, see the same
error and shrug it off?

Why not do a 

loc_finite = WHERE( FINITE( test ) EQ 1, count_finite )
IF ( count_finite GT 0 ) THEN $
  sum = TOTAL( test[ loc_finite ] > 0.0 ) $
ELSE $
  sum = !VALUES.F_NAN  ; Or some other suitable flag

??

IDL> print, sum
      7.00000

Oh, and make sure you set !EXCEPT = 2 in your idl setup file. That'll learn ya to remove
errors from your code :o)

paulv

-- 
Paul van Delst           A little learning is a dangerous thing;
CIMSS @ NOAA/NCEP        Drink deep, or taste not the Pierian spring;
Ph: (301)763-8000 x7274  There shallow draughts intoxicate the brain,
Fax:(301)763-8545        And drinking largely sobers us again.
paul.vandelst@noaa.gov                   Alexander Pope.