[ncl-talk] Re: Strange error

Hi Saji,

First a simple answer to the 64-bit machine question:

On a 64-bit machine you can have bigger integer numbers using NCL. You
just need to create them as longs. Currently the only way to do this is
to
use the 'new' operator.

Using your original example you would say:

ncl 5> a = new(1, long)
ncl 6> a = 35280
ncl 7> print(a * 192 * 96 * 4)
(0) 2601123840

or (showing variable 'a' in detail)

ncl 8> a = a * 192 * 96 * 4
ncl 9> print(a)

Variable: a
Type: long
Total Size: 8 bytes
             1 values
Number of Dimensions: 1
Dimensions and sizes: [1]
Coordinates:
Number Of Attributes: 1
   _FillValue : -9999
(0) 2601123840

Now as to why NCL does not give error messages when you have integer
overflow, it is because it directly uses
the underlying C libraries to perform the arithmetic. They don't give
an error message in this situation so neither
does NCL. I realize that languages like Ruby and Python may be more
user friendly in this regard, but you have
to realize that in an array processing environment like NCL testing for
overflow on every calculation would
likely impose a significant cost in performance. It may interest you to
know (I think this is correct) that the NumPy
array package for Python does no overflow checking for integers either.
On the other hand, because it is a mandated
feature of IEEE floating point arithmetic, there is overflow checking
(as well as other types of checking) for floating
point values in NumPy.

I realize that the absence of big integers in 32 bit environments is
becoming more of an issue. We expect this
to be solved in the relatively near future as we implement full support
for NetCDF 4. This support will require
that we implement a complete set of explicitly sized integer types (8,
16, 32, 64 signed and unsigned) that will
not change (as the long type does now) on different platforms.
Hope this helps.
  -dave

On May 2, 2007, at 6:29 AM, Saji Hameed wrote:

>
>
> Begin forwarded message:
>
>>
>> From: Saji Njarackalazhikam Hameed <saji_at_apcc21.net>
>> Date: May 2, 2007 9:34:13 AM GMT+09:00
>> To: Mary Haley <haley_at_ucar.edu>
>> Cc: David Brown <dbrown_at_ucar.edu>, Rick Grubin <grubin_at_ucar.edu>
>> Subject: Re: [ncl-talk] Strange error
>>
>>
>> Hi Mary,
>>
>> Thank you for replying and passing on the message to the NCL
>> developers.
>>
>> You are right. But it will be nice, if NCL can return an error
>> message, instead of erroneous values. An NCL programmer may not
>> be careful (as in my case) and may erroneously use an expression that
>> may yield
>> an integer number bigger than 2^31.
>>
>>  o What about a 64-bit machine? Shouldn't NCL compiled for 64-bit
>>   machines hold bigger integer numbers ? I get the same values in
>>   our 64-bit machine, running NCL 64-bit binary.
>>
>>  o I was using this to calculate something in the context of
>> outputting
>>   a huge netcdf file. Since NCL has support for outputting (am i
>> wrong)
>>   large netcdf files (>2GB), it may be appropriate to have some
>> support
>>   for Big Numbers.
>>
>>   - It would be nice, if NCL can automatically convert the type in
>> such
>>   situations from ordinary integer to one that can hold Bigger Numbers
>>   (i am not conversant with this terminology, so i am afraid my
>> statement
>>   may not be clear). Anyway here is an example calculation in Ruby
>> that
>>   illustrates this concept
>>
>>
>>   irb(main):001:0> a=35280
>>   => 35280
>>   irb(main):002:0> b=a*192*96*4
>>   => 2601123840
>>   irb(main):003:0> puts a.class
>>   Fixnum
>>   => nil
>>   irb(main):004:0> puts b.class
>>   Bignum
>>   => nil
>>
>>
>>
>> Best wishes,
>>
>> saji
>>
>> p.s: We have now set up an automatic climate monitoring system
>> at the APEC Climate Center that is completely based
>> on NCL (some glue code is written in Ruby though + NCO is used). The
>> system accesses specified servers (some of them openDAP) and retrieves
>> just the right amount of data everyday at 3pm local time, does
>> appropriate
>> analyses and plots some specified figures, all without human
>> intervention.
>>
>> Only possible because of NCL!
>>
>>
>>
>> * Mary Haley <haley_at_ucar.edu> [2007-05-01 08:44:26 -0600]:
>>
>>>
>>> Hi Saji,
>>>
>>> My apologies for letting this one slip. I'm CC-ing our NCL developers
>>> to make sure I have this correct. I think the simple fact of the
>>> matter is that these are integers, and you can't have an integer that
>>> is bigger than 2^31.
>>>
>>> --Mary
>>>
>>> On Thu, 26 Apr 2007, Saji Njarackalazhikam Hameed wrote:
>>>
>>>>
>>>> Dear All,
>>>>
>>>> I got this strange and a bit frightening values for the
>>>> following calculation.
>>>>
>>>> ncl 0> a=35280
>>>> ncl 1> print(a*192*96*4)
>>>> (0) -1693843456
>>>>
>>>>
>>>> I believe that this is because the limit for integer values is
>>>> reached, but
>>>> should not NCL return an error or warning message for this.
>>>>
>>>> ; Making the numbers floats would give the right value.
>>>> ;
>>>> ; ncl 2> print(a*192*96*4.)
>>>> ; (0) 2.601124e+09
>>>>
>>>> I am using NCL version 4.2.0.a035 on a Linux machine.
>>>>
>>>> saji
>>>> ...
>>>>
>>>> --
>>>> Saji N. Hameed
>>>>
>>>> APEC Climate Center +82 51 668 7470
>>>> National Pension Corporation Busan Building 12F
>>>> Yeonsan 2-dong, Yeonje-gu, BUSAN 611705 saji_at_apcc21.net
>>>> KOREA
>>>> _______________________________________________
>>>> ncl-talk mailing list
>>>> ncl-talk_at_ucar.edu
>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>
>>
>> --
>> Saji N. Hameed
>>
>> APEC Climate Center +82 51 668 7470
>> National Pension Corporation Busan Building 12F
>> Yeonsan 2-dong, Yeonje-gu, BUSAN 611705
>> saji_at_apcc21.net
>> KOREA
>>
>>

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Received on Fri May 04 2007 - 11:32:20 MDT