# Re: summation problem

```Jaco van Gorkom wrote:
>
> Paul van Delst wrote:
> > 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?
> > >
> > > 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:
> >
> > 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?
>
> That is *exactly* what I'd do: shrug it off! The log of a -ve number gives me
> -Inf as a
> result, which will propagate through any calculation to be NaN, Inf, or -Inf.
> Just another
> missing data point.

:o)

> > 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
>
> Of course I see your point. I would probably implement a FINITE() check if I
> were writing a
> full program, but the annoying special-case programming for when WHERE() returns
> -1 held me
> back here.

Hence the use of count_finite. Then it doesn't matter what is returned by WHERE() in
loc_finite.

> On second thought: WHERE() could only return -1 for a day without sunrise...

I'm sure there are some Laplanders that use IDL :o) And there's those Antarctic folk.

> > Oh, and make sure you set !EXCEPT = 2 in your idl setup file. That'll learn ya to remove
> > errors from your code :o)
>
> Geez! Thanks for pointing that out! This solves everything Manish: !EXCEPT = 0.

Oof! That hurtz.

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.
```