[ncl-talk] unexpected results from very simple code

[Dennis Shea]

ncl 0> degrees = (/210200051, 121, 36, 43,38,58,26/)
ncl 1> print(typeof(degrees))   ; integer

Why did you use 'sprintf' to print an integer?
         print(sprintf("%9.0f",degrees(0)))
Please note the documentation.
---
http://www.ncl.ucar.edu/Document/Functions/Built-in/sprintf.shtml
Converts floats or doubles into formatted strings.
---
http://www.ncl.ucar.edu/Document/Functions/Built-in/sprinti.shtml
Converts integers into formatted strings.
---

ncl 2> print(sprinti("%10.0i",degrees(0)))

(0)      210200051

On Mon, Jul 20, 2015 at 9:19 PM, Rick Brownrigg <brownrig at ucar.edu> wrote:
> Hi Hongyan,
>
> As Arne indicated, with 32-bit floating point, you can't expect more than 7
> significant digits (14 for double), and in your case, you are asking for
> precision 2 orders of magnitude beyond that.
>
> For the truly curious, all the gory reality about computing and
> precision/accuracy is detailed in this doc:
>
> http://www.cse.msu.edu/~cse320/Documents/FloatingPoint.pdf
>
> HTH...
> Rick
>
> On Mon, Jul 20, 2015 at 7:26 PM, danghy at gmail.com <danghy at gmail.com> wrote:
>>
>> Hi Arne,
>>
>> Thanks a lot for the information!  I will probably use "integer" to solve
>> the problem.  But I was really curious why the floating point number returns
>> "210200048", not "210200049"... the perfect case would be that it returns
>> "210200051".
>>
>> Thanks again.
>>
>> Hongyan
>> ________________________________
>> danghy at gmail.com
>>
>>
>> From: Arne Melsom
>> Date: 2015-07-20 17:27
>> To: danghy
>> CC: ncl-talk
>> Subject: Re: [ncl-talk] unexpected results from very simple code
>> Hi Danghy,
>>
>> I think that you can't expect (4 byte) floating point numbers to deliver
>> the accuracy (no. digits) that you request. In your case, I suggest using
>> double precision or integer representation. Here's a part of your example
>> using the original representation and the two alternatives:
>>
>> begin
>>
>> a=210200051.
>> print("output / a :")
>> print(tostring(a))
>> print(sprintf("%9.0f",a))
>>
>> ad=210200051.d
>> print("output / ad:")
>> print(tostring(ad))
>> print(sprintf("%9.0f",ad))
>>
>> ai=210200051
>> print("output / ai:")
>> print(tostring(ai))
>> print(sprinti("%9i",ai))
>>
>> end
>>
>>
>> ...which gives the following output:
>>
>> (0) output / a :
>> (0) 210200048.000000
>> (0) 210200048
>> (0) output / ad:
>> (0) 210200051.000000
>> (0) 210200051
>> (0) output / ai:
>> (0) 210200051
>> (0) 210200051
>>
>> Hope this helps!
>> Arne M.
>>
>>
>>
>> ----- Original Message -----
>> > Dear all,
>> >
>> > I met a problem when reading "station ID" - I've simplified the code as
>> > follows:
>> >
>> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> > load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> > begin
>> >
>> > degrees = (/210200051, 121, 36, 43,38,58,26/)
>> >
>> > print(sprintf("%9.0f",degrees(0)))
>> > print(tostring(degrees(0)))
>> >
>> > a=210200051.
>> > print(tostring(a))
>> > print(sprintf("%9.0f",a))
>> >
>> > end
>> >
>> > The NCL output on screen is:
>> >
>> > ncl test.ncl
>> > Copyright (C) 1995-2015 - All Rights Reserved
>> > University Corporation for Atmospheric Research
>> > NCAR Command Language Version 6.3.0
>> > The use of this software is governed by a License Agreement.
>> > See http://www.ncl.ucar.edu/ for more details.
>> > (0) 210200048
>> > (0) 210200051
>> > (0) 210200048.000000
>> > (0) 210200048
>> >
>> > Only the second method "tostring" gives the correct station ID. Could
>> > you
>> > please give me a clue why is this happening?
>> >
>> > Appreciate!
>> >
>> >
>> > danghy at gmail.com
>> >
>> > _______________________________________________
>> > ncl-talk mailing list
>> > ncl-talk at ucar.edu
>> > List instructions, subscriber options, unsubscribe:
>> > http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>> >
>>
>>
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>
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