find関数について

pix   = 0.001;        
a = -1:pix:1; 
find(a==0.1)

ans =

  1×0 empty double row vector

配列aには0.1が格納されているにもかかわらず，findでインデックスを得ることができません．

ほかに要素のインデックスを得る方法がありましたら教えていただけると幸いです．

Answer 1

[Dyuman Joshi]

Welcome to the world of floating point numbers, where not all numbers can be represented exactly in binary form.

See this thread for more information - https://in.mathworks.com/matlabcentral/answers/57444-why-is-0-3-0-2-0-1-not-equal-to-zero?s_tid=faqs_link

When comparing floating point numbers, the best practice is to use a tolerance -

pix = 0.001;        
a = -1:pix:1;

tol = 1e-6;
idx = find(abs(a - pix) < tol)

idx = 1002

%check
a(idx)

ans = 0.0010

You can also use ismembertol -

k = ismembertol(a, pix);
IDX = find(k)

IDX = 1002