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Re: average of a function


From: Henry F. Mollet
Subject: Re: average of a function
Date: Tue, 09 Nov 2004 09:31:06 -0800
User-agent: Microsoft-Entourage/10.1.1.2418

Hacking my way to a close enough? solution compared to answer below and the
one provided by P.K.
Henry
octave:8> t=(-1:0.01:5/2);
octave:9> y = t.^2 - 5.*t + 6*cos(pi*t);
octave:10> mean(y)
ans = -1.6253
octave:11> plot (t,y,"x")
octave:12> t=(-1:0.001:5/2);
octave:13> y = t.^2 - 5.*t + 6*cos(pi*t);
octave:14> mean(y)
ans = -1.6214
octave:15> t=(-1:0.0001:5/2);
octave:16> y = t.^2 - 5.*t + 6*cos(pi*t);
octave:17> mean(y)
ans = -1.6210
octave:18> format long
octave:19> mean(y)
ans = -1.62103554930008
octave:20> quad('x', -1, 5/2)/(5/2 - -1)
ans = -1.62099257606588

*** local user variables: % at the end

prot  type                       rows   cols  name
====  ====                       ====   ====  ====
 rwd  range                         1  35001  t
 rwd  matrix                        1  35001  y



on 11/9/04 2:10 AM, (Ted Harding) at address@hidden wrote:

> On 09-Nov-04 Fred J. wrote:
>> Hello
>> 
>> debian 2.6.8 i686-pc-GNU/Linux
>> GNU Octave, version 2.1.60
>> 
>> I just started with octave, and appreciate some help
>> with this simple
>> task, could not get much help from reading the FAQs
>> and the manual.
>> 
>> OK, 
>> I need to determine the average value of this function
>> which I expect
>> it to be -1.620993 but I am getting a different ans
>> and not sure if I am
>> using octave correctly.
>> 
>> octave> function y=x(t), y = t^2 - 5*t + 6*cos(pi*t);
>> end;
>> octave> quad('x', -1, 5/2)
>> ans = -5.6735
> 
> If I've understood correctly, your code returns the numerical *integral*
> of x(t) over the range (-1,2.5). The length of this range is 3.5.
> 
> The *average* of the function is the integral divided by the length
> of the range. With your numerical answer I get
> 
> (-5.6735)/3.5 = -1.621
> 
> which is very close to the value (-1.620993) that you expected to get.
> 
> Best wishes,
> Ted.
> 
> 
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <address@hidden>
> Fax-to-email: +44 (0)870 094 0861  [NB: New number!]
> Date: 09-Nov-04                                       Time: 10:10:21
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> 
> 
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