Re: print() precision

Fan,

Hmmm. We explained in different ways that many decimal numbers can
not be stored exactly in floats and doubles, there is a loss of
precision on input. This is basic math, and has nothing to do with
NCL in particular. This is true even for absurdly simple numbers like
0.1.

We also showed you several ways of displaying variables with increased
precision, including more than necessary precision so you could be
sure to get all SIGNIFICANT decimal digits.

So what more are you looking for in a new function? I think if you
show another very simple example, with the EXACT string output that
you would like to see, we can reach a better understanding.

--Dave
(Please reply only to user list, thank you.)

On Wed, Jul 31, 2013 at 5:32 PM, Fang, Fan (GSFC-610.2)[ADNET SYSTEMS
INC] <fan.fang-1@nasa.gov> wrote:
> Thanks Wei and everyone for investigating this.
>
> However not under all situations do we know the value of a double or want to format it. It'd be great if NCL has a function that prints exactly what the float or double value a variable holds, like treating it as a string.
>
> -Fan
> ________________________________________
> From: Wei Huang [huangwei@ucar.edu]
> Sent: Wednesday, July 31, 2013 3:39 PM
> To: Fang, Fan (GSFC-610.2)[ADNET SYSTEMS INC]
> Cc: Dennis Shea; ncl-talk@ucar.edu
> Subject: Re: print() precision
>
> Fan,
>
> NCL uses "%g" in its C program to print float or double.
> This will give 6 digit when print, or convert to string.
>
> The program below can clearly demonstrate that.
>
> If you need more accurate print, please use the sprintf function
> (also shown in program below).
>
> Wei
>
> ---------------
> a = 1.0d
> b = 11.11d
>
> do n = 0, 20
> print("No. " + n + ": a(%g) = " + a + ", a(%32.16f) = " + sprintf("%32.16f", a))
>
> a = a * b
> end do
>
> a = 1.0d
> b = 0.1111d
>
> do n = 0, 20
> print("No. " + n + ": a(%g) = " + a + ", a(%32.16f) = " + sprintf("%32.16f", a))
>
> a = a * b
> end do
>
>
> huangwei@ucar.edu
> VETS/CISL
> National Center for Atmospheric Research
> P.O. Box 3000 (1850 Table Mesa Dr.)
> Boulder, CO 80307-3000 USA
> (303) 497-8924
>
>
> On Jul 31, 2013, at 10:14 AM, Fan Fang <Fan.Fang@nasa.gov> wrote:
>
>> Thanks Wei and Dennis.
>>
>> It works. But if the variable is pre-assigned without 'd' at the end,
>> would 'todouble()' somehow do it? I have
>>
>> begin
>> a = 0.4071155678
>> b = todouble(a)
>> print(b)
>> end
>>
>> and I got something not quite precise:
>>
>> Copyright (C) 1995-2010 - All Rights Reserved
>> University Corporation for Atmospheric Research
>> NCAR Command Language Version 5.2.1
>> The use of this software is governed by a License Agreement.
>> See http://www.ncl.ucar.edu/ for more details.
>>
>>
>> Variable: b
>> Type: double
>> Total Size: 8 bytes
>> 1 values
>> Number of Dimensions: 1
>> Dimensions and sizes: [1]
>> Coordinates:
>> (0) 0.4071155786514282
>>
>>
>> On 07/31/2013 12:07 PM, Dennis Shea wrote:
>>> xf = 0.4071155678
>>> xd = 0.4071155678d
>>>
>>> print("xf="+xf +" : "+sprintf("%13.6f", xf))
>>> print("xd="+xd +" : "+sprintf("%13.10f", xd))
>>>
>>> ==============
>>>
>>> (0) xf=0.407116 : 0.407116
>>> (0) xd=0.407116 : 0.4071155678
>>>
>>>
>>> On 7/31/13 9:57 AM, Wei Huang wrote:
>>>> Fan,
>>>>
>>>> Try
>>>>
>>>> print(0.407115567890123456789d)
>>>>
>>>> Wei
>>>>
>>>> huangwei@ucar.edu
>>>> VETS/CISL
>>>> National Center for Atmospheric Research
>>>> P.O. Box 3000 (1850 Table Mesa Dr.)
>>>> Boulder, CO 80307-3000 USA
>>>> (303) 497-8924
>>>>
>>>>
>>>> On Jul 31, 2013, at 9:41 AM, Fan Fang <Fan.Fang@nasa.gov> wrote:
>>>>
>>>>> It appear print() only does floats. IS there an easy way to print out
>>>>> just what is fed?
>>>>>
>>>>> -Fan
>>>>>
>>>>> begin
>>>>> print(0.4071155678)
>>>>> end
>>>>>
>>>>> (0) 0.4071156
_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Wed Jul 31 19:54:22 2013