integrating trig functions with large constants, exponent out of range
Subject: integrating trig functions with large constants, exponent out of range
From: Raymond Toy
Date: Fri, 05 Jan 2007 23:03:25 -0500
Daniel Lakeland wrote:
> On Fri, Jan 05, 2007 at 03:51:45PM -0800, Daniel Lakeland wrote:
>
>> On Sat, Jan 06, 2007 at 01:10:07AM +0200, Neilen Marais wrote:
>>
>>> Hi
>>>
>>> I get the following problem:
>>>
>>>
>>> I tried reducing the error:
>>>
>>> (%i9) integrate(%i*sin(34037595938027*x3)*x3, x3);
>>>
>>> but had to interrupt it since it seemed to take forever. I found that
>>> the integration time is dependent on the size of the constant in the
>>> expression. integrate(%i*sin((3*x3))*x3, x3) happens fast,
>>> integrate(%i*sin((30000*x3))*x3, x3) takes several seconds etc.
>>>
>> This executes in no time flat for me on windows stock maxima 5.10.0 in
>> GCL.
>>
>> ****** It also gives a wrong answer!!! ******
>>
>>
>
> The debian package 5.10.0-6 on amd64 has the same hanging behavior
> that you see rather than the fast wrong answer.
>
>
I don't know the real reason, but I suspect it's caused by compiling the
code with safety low enough that gcl doesn't check to see if the result
of multiplication is a fixnum. At least that's the case with clisp and
cmucl.
For amd64, I assume most-positive-fixnum is close to 64 bits instead of
32, so issue isn't reached, at least as quickly.
Ray