Re: possible bug with gc_latlon

Hi Matt,

Thanks so much for providing the files and script up front.

I ran this on my 64-bit Mac and a 64-bit LINUX box, and got "Nan" on both of them.

On a 32-bit Linux box, I got 0.

I've filed a ticket for this (NCL-995) and will look at it shortly.

--Mary

On Feb 9, 2011, at 6:15 PM, Matthew Higgins wrote:

> Hi all,
>
> I think I may have found a platform-dependent bug with gc_latlon. I've
> found that when my input latitude and longitudes are the identical,
> rather than having a 0 returned (as in a distance of 0 km between the
> two points), occasionally I will get an NaN returned. I only see this
> issue if I'm running on a Cray XE6 - when I run the same code on my
> local linux box, I get a 0. In both cases I am running NCL 5.2.1.
>
> Here is some example code. NCAR NCL folks - I have uploaded the two
> .nc files referenced in the code below to the CGD ftp site if you'd
> like to try to replicate what I am seeing.
>
> Matt
>
> Here's the script:
>
> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
> f1 = addfile("geo_em.d01.50km.nc", "r")
> lat2d_50 = f1->XLAT_M(0,:,:)
> lon2d_50 = f1->XLONG_M(0,:,:)
> lat1d_50 = ndtooned(lat2d_50)
> lon1d_50 = ndtooned(lon2d_50)
> f2 = addfile("geo_em.d01.100km.nc", "r")
> lat2d_100 = f2->XLAT_M(0,:,:)
> lon2d_100 = f2->XLONG_M(0,:,:)
> lat1d_100 = ndtooned(lat2d_100)
> lon1d_100 = ndtooned(lon2d_100)
>
> i = 5832
> q = 23532
>
> print("example lat/lon in 100km grid "+lat1d_100(i)+" "+lon1d_100(i))
> print("example lat/lon in 50km grid "+lat1d_50(q)+" "+lon1d_50(q))
> dist = gc_latlon(lat1d_100(i),lon1d_100(i),lat1d_50(q),lon1d_50(q),2,4)
> print("distance in km between these points is "+dist)
>
>
>
> --
> Matt Higgins
> Cooperative Institute for Research in Environmental Sciences
> University of Colorado - Boulder
> (303) 735-1636
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Received on Fri Feb 11 09:27:53 2011