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Groups > comp.graphics.apps.gnuplot > #1057 > unrolled thread

fatal precision problem in gnuplot or fatal operator incompetence?

Started by"Charles T. Smith" <cts.private@yahoo.com>
First post2012-04-28 12:25 +0200
Last post2012-04-28 16:43 +0200
Articles 6 — 3 participants

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  fatal precision problem in gnuplot or fatal operator incompetence? "Charles T. Smith" <cts.private@yahoo.com> - 2012-04-28 12:25 +0200
    Re: fatal precision problem in gnuplot or fatal operator incompetence? 3031-866 <cts.private@yahoo.com> - 2012-04-28 13:33 +0200
      Re: fatal precision problem in gnuplot or fatal operator incompetence? brendan.halpin@ul.ie (Brendan Halpin) - 2012-04-28 15:33 +0100
        Re: fatal precision problem in gnuplot or fatal operator incompetence? "Charles T. Smith" <cts.private@yahoo.com> - 2012-04-28 16:45 +0200
    Re: fatal precision problem in gnuplot or fatal operator incompetence? brendan.halpin@ul.ie (Brendan Halpin) - 2012-04-28 15:31 +0100
      Re: fatal precision problem in gnuplot or fatal operator incompetence? "Charles T. Smith" <cts.private@yahoo.com> - 2012-04-28 16:43 +0200

#1057 — fatal precision problem in gnuplot or fatal operator incompetence?

From"Charles T. Smith" <cts.private@yahoo.com>
Date2012-04-28 12:25 +0200
Subjectfatal precision problem in gnuplot or fatal operator incompetence?
Message-ID<jnggj3$s2a$1@online.de>
Why does:

   plot [0:1000] sin(x)

seem to be modulated with what appears to be a sine wave?

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#1058

From3031-866 <cts.private@yahoo.com>
Date2012-04-28 13:33 +0200
Message-ID<jngkj2$umr$1@online.de>
In reply to#1057
On 04/28/12 12:25, Charles T. Smith wrote:
> Why does:
>
> plot [0:1000] sin(x)
>
> seem to be modulated with what appears to be a sine wave?


Could this have anything to do with the fact that when I plot:


gnuplot> set parametric
gnuplot> set size square
gnuplot> r(t) = 1 - exp(-0.25*t/pi)   # the radius as function of t
gnuplot> plot [0:25*pi][-1.1:1.1][-1.1:1.1] r(t)*cos(t), r(t)*sin(t)

(from Gnuplot In Action, by Philipp K. Janert)

I get a spiral of straight lines rather than a curving spiral, as shown 
in the book?

Is this a reason to be using 64 bit linux?

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#1060

Frombrendan.halpin@ul.ie (Brendan Halpin)
Date2012-04-28 15:33 +0100
Message-ID<87haw4lydm.fsf@wivenhoe.ul.ie>
In reply to#1058
On Sat, Apr 28 2012, 3031-866 wrote:

> On 04/28/12 12:25, Charles T. Smith wrote:
>> Why does:
>>
>> plot [0:1000] sin(x)
>>
>> seem to be modulated with what appears to be a sine wave?
>
>
> Could this have anything to do with the fact that when I plot:
>
>
> gnuplot> set parametric
> gnuplot> set size square
> gnuplot> r(t) = 1 - exp(-0.25*t/pi)   # the radius as function of t
> gnuplot> plot [0:25*pi][-1.1:1.1][-1.1:1.1] r(t)*cos(t), r(t)*sin(t)
>
> (from Gnuplot In Action, by Philipp K. Janert)
>
> I get a spiral of straight lines rather than a curving spiral, as shown
> in the book?

Yes, exactly so. Insert "set samples 10000" and you'll get your spiral.

>
> Is this a reason to be using 64 bit linux?

No. 

Brendan

-- 
Brendan Halpin,   Department of Sociology,   University of Limerick,   Ireland
Tel: w +353-61-213147  f +353-61-202569  h +353-61-338562;  Room F1-009 x 3147
mailto:brendan.halpin@ul.ie    ULSociology on Facebook: http://on.fb.me/fjIK9t
http://teaching.sociology.ul.ie/bhalpin/wordpress         twitter:@ULSociology

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#1062

From"Charles T. Smith" <cts.private@yahoo.com>
Date2012-04-28 16:45 +0200
Message-ID<jngvrd$6qj$2@online.de>
In reply to#1060
On 04/28/12 16:33, Brendan Halpin wrote:
> On Sat, Apr 28 2012, 3031-866 wrote:
>
>> On 04/28/12 12:25, Charles T. Smith wrote:
>>> Why does:
>>>
>>> plot [0:1000] sin(x)
>>>
>>> seem to be modulated with what appears to be a sine wave?
>>
>>
>> Could this have anything to do with the fact that when I plot:
>>
>>
>> gnuplot>  set parametric
>> gnuplot>  set size square
>> gnuplot>  r(t) = 1 - exp(-0.25*t/pi)   # the radius as function of t
>> gnuplot>  plot [0:25*pi][-1.1:1.1][-1.1:1.1] r(t)*cos(t), r(t)*sin(t)
>>
>> (from Gnuplot In Action, by Philipp K. Janert)
>>
>> I get a spiral of straight lines rather than a curving spiral, as shown
>> in the book?
>
> Yes, exactly so. Insert "set samples 10000" and you'll get your spiral.
>
>>
>> Is this a reason to be using 64 bit linux?
>
> No.
>
> Brendan
>


Thank you for the complete and concise answers.

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#1059

Frombrendan.halpin@ul.ie (Brendan Halpin)
Date2012-04-28 15:31 +0100
Message-ID<87mx5wlygu.fsf@wivenhoe.ul.ie>
In reply to#1057
On Sat, Apr 28 2012, Charles T. Smith wrote:

> Why does:
>
>   plot [0:1000] sin(x)
>
> seem to be modulated with what appears to be a sine wave?

The long answer involves words like aliasing and Nyquist. 

The short answer is evident from the following:

set samples 10000
plot [0:1000] sin(x)

Brendan
-- 
Brendan Halpin,   Department of Sociology,   University of Limerick,   Ireland
Tel: w +353-61-213147  f +353-61-202569  h +353-61-338562;  Room F1-009 x 3147
mailto:brendan.halpin@ul.ie    ULSociology on Facebook: http://on.fb.me/fjIK9t
http://teaching.sociology.ul.ie/bhalpin/wordpress         twitter:@ULSociology

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#1061

From"Charles T. Smith" <cts.private@yahoo.com>
Date2012-04-28 16:43 +0200
Message-ID<jngvmu$6qj$1@online.de>
In reply to#1059
On 04/28/12 16:31, Brendan Halpin wrote:
> On Sat, Apr 28 2012, Charles T. Smith wrote:
>
>> Why does:
>>
>>    plot [0:1000] sin(x)
>>
>> seem to be modulated with what appears to be a sine wave?
>
> The long answer involves words like aliasing and Nyquist.


Excellent.  That's on my self-study plan.


>
> The short answer is evident from the following:
>
> set samples 10000
> plot [0:1000] sin(x)
>
> Brendan

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