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Re: Numeric issue
From: |
Marco Atzeri |
Subject: |
Re: Numeric issue |
Date: |
Fri, 04 Jul 2014 16:33:14 +0200 |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
On 04/07/2014 11:46, JokerOne wrote:
Hi community,
I using Octave for quite a while now, however, apparently, I am not aware of
some numeric issues going on, which is where I like to ask you for help:
Basically, I noticed, that in the following dummy code, the results appear
strange to me:
clear all;
format long;
a = [1.1:1.1:100];
a(50) % expected to be == 55
b = 50*1.1; % expected to be == 55
octave:7> 50*1.1
ans = 55.000
((a(50)-b) == 0) % is 1
((a(50)-55) == 0) % is 0 (!?)
this check is always questionable on any numerical operation,
due to rounding precision.
On my system:
octave:10> a(50)-55
ans = 7.1054e-15
ceil(a(50)) % expected to be == 55, but results in 56 ??
ceil(b) % same as above ??
ceil(55) % == 55, as expected
for the reason above the ceiling is 56....
Regards
Marco