MATLAB: Is this Matlab bug or error? anyone who can help

bug reportfloating pointfloating point numbernot a bug

I'm using Matlab to solve some problems.

and I realized sth went wrong

that is like this

stepsize =0.05;
theta = (0:-stepsize:-180+stepsize)*pi/180;
%I'm looking for -90 degree
find(theta == -90*pi/180)

the answer is

ans =

1×0 empty double row vector

What's wrong with me??

Best Answer

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Related Solutions

MATLAB: Simple miscalculation: (1-0.95)*4000 = 2.000000000000002e+02

This is not a bug, nor is it a mistake. This is the normal behavior of floating point numbers, and although it is not at all unexpected it often confuses beginners.

MATLAB uses floating point numbers which are stored with a finite number of binary digits. Because of the finite precision of these numbers, calculations often incur some rounding error, and it is your job as the programmer to account for this in the design of your algorithm.

If you really absolutely must avoid the precision limits of the standard number classes, then you basically have two choices:

use a symbolic mathematics tool, such as the Symbolic Toolbox.
use a higher precision toolbox, such as John D'Errico's HPF. Note that infinite precision is impossible.

For more information read these:

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

http://de.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

You might like to try James Tursa's FEX submission too:

http://de.mathworks.com/matlabcentral/answers/41536-why-is-2-24-10-22-4-not-equal-to-0

MATLAB: Didn’t I get “Hello” word by running following script? if I change the value in if loop except 13.2 it gives me correct answer.

clc
tol = 10^-3 ;
display('code executing');
for number=1:0.1:15
    if abs(number-13.2)<=tol
        disp('Hello');
    end 
end

You should not compare flottant numbers using ==..you should subtract and check is the absolute value of difference is less then a specified tolerance.

Best Answer

Related Solutions

MATLAB: Simple miscalculation: (1-0.95)*4000 = 2.000000000000002e+02

MATLAB: Didn’t I get “Hello” word by running following script? if I change the value in if loop except 13.2 it gives me correct answer.

Related Question