MATLAB: A simple “bug” in finding an element in an array using find()

floating pointMATLABmatrix manipulationnot a bug

Hi, I am not sure if it is a bug in matlab, but when I just simply try to find an element in an array:

list=-1:0.1:1;
find(list=0.1)

I get an strange result which is Empty matrix: 1-by-0. Instead, if I try find(list=0.6), I get the correct result 17.

Anyone have any idea?

Welcome to floating-point approximation error, and the way the colon operator works.

Try this:

list=-1:0.1:1;
find(list<=0.1,1,'last')

You are seeing the effects of floating-point approximation error.

% input
N = 5 ; M = 4 ; 
a = [1 3 ; 2 4 ; 1 4 ; 1 2 ; 3 4]
% engine in one line
XX = full(sparse(repmat(1:N, size(a,2), 1)', a, 1,N,M))