min function why do results change for numbers with decimal values?

ex1:

X=[1:11];
Y=double( 1.0*X);
diffY                      = diff(Y); 
[diffY_min,diffY_index]   = min (diffY);

ans diffY_min = 1 diffY_index=1

ex2:

X=[1:1.4:15];
Y=double( 1.0*X);
diffY                      = diff(Y); 
[diffY_min,diffY_index]   = min (diffY); 

ans diffY_min = 1.4 diffY_index=8

all numbers are double prec. Why does min treat numbers N.xxx different than N? Get similar results if I change slope fm 1 to 2.1 or sqrt(2) or any value that results in diffY .NE. 1,2,3....

[SteveH]

thanks. That explains why the diff values aren't exactly equal.

Answer 1

[Walter Roberson]

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

Answer 2

[Stephen23]

When you compare floating point numbers (such as using == or unique) you should use a tolerance value like this:

>> tol = 1e-3;
>> abs((0.05+0.01) - 0.06) <= tol
ans =
     1

And you should read about floating point numbers to know why this is required:

http://www.mathworks.com/help/matlab/matlab_prog/floating-point-numbers.html

http://www.mathworks.com/matlabcentral/answers/69-why-does-1-2-3-1-3-not-equal-zero

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

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

http://www.mathworks.com/company/newsletters/news_notes/pdf/Fall96Cleve.pdf

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

https://www.mathworks.com/matlabcentral/newsreader/view_thread/66553

http://www.mathworks.com/company/newsletters/news_notes/pdf/Fall96Cleve.pdf

http://blogs.mathworks.com/loren/2006/08/23/a-glimpse-into-floating-point-accuracy/

http://www.mathworks.com/help/fixedpoint/ug/floating-point-numbers.html

And some external links on this topic:

http://www.lahey.com/float.htm

http://matlabgeeks.com/tips-tutorials/floating-point-comparisons-in-matlab/

[SteveH]

thanks