| Re: 1e38 limit? [message #65415 is a reply to message #65323] |
Sat, 28 February 2009 02:49  |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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Paula schrieb:
> i think i found it, but i'm not sure how to explain...
>
> i have a loop (integer) that goes through a list of files, reading
> data and computing stuff. i added a 'print,loop' line to the code, and
> could see the routine would get stuck in one specific file, staying
> there forever. thus i opened this file in IDL prompt and went through
> all the steps of the routine one by one. doing the things via prompt,
> i was getting an underflow message when reaching a line
>
> pdf = exp(-0.5*chi)
>
> because for the data inside that (only) file, the 1d40 factor i had
> applied before was too large and chi ended up of the order of 1e4, and
> then pdf would end up equal to 0 + underflow.
>
> but, why running the routine automatically the code would get stuck
> there, instead of giving the underflow message and moving on,
because you haven't implemented an error handler.
look also on compile_opt
There is one to force the default type to become double.
cheers
Reimar
i don't
> know. i can guess the zero-ed array ended up producing a NaN array
> somewhere later in the routine that messed the things up. to be honest
> i haven't gone further as i stopped to improve the code, so that i
> will test/treat the data on-the-fly and avoid the underflow in the
> first place :).
>
>
> anyway, i had to change a couple of 'e' to 'd' in the code indeed, as
> you pointed out. as well as creating a double-precision array to read
> the data from the asc files (it was float before and some numbers were
> being lost without me realising it).
>
> paula
>
> On Feb 27, 6:39 pm, Chris <beaum...@ifa.hawaii.edu> wrote:
>> The overflow, by itself, shouldn't result in an infinite process - idl
>> should just complain about floating point overflow maybe.
>>
>> What COULD be happening is that you have a loop in your code. You are
>> using a floating point value as the loop variable, and incrementing it
>> by a number much smaller than itself. When that happens, there isn't
>> enough precision to store the difference between the numbers before
>> and after increment, and the loop variable stays the same forever.
>> It's actually a floating point UNDERFLOW.
>>
>> Maybe? any floating point loops?
>>
>> chris
>
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