How to select the first appearance of the minimum value?

I have a vector (A) with some numbers, then I want to find which one is the closest to the value b.

A=[-0.1000   -0.0800   -0.0600   -0.0400   -0.0200   0   0.0200    0.0400    0.0600    0.0800    0.1000];%dummy data
b=-0.03;

In this case, both -0.04 and -0.02 are at the same distance, then I want to select -0.04

I tried several methods, but for some reason, Matlab completely ignores the possibility of -0.04

nearest=b %initialisation
difference= abs(A-b)           
minimum=min(difference)
for i=1:length(A)
   if minimum == difference(i) %technically it should enter this if twice, however, it doesnt enter once!
       nearest=A(i)
   end
end
nearest

I am so frustrated, technically, this line of code should return all the appereances, so two, but it only returns one!

[row,col] = find(difference==val)

I will really appreciate some help with this. Clearly I am doing something wrong, but I have no clue what.

[jessupj]

your problem is related to floating point errors:

d=abs(A-b)
norm(d(4)-d(5))

3.46944695195361e-18

that's why it's only returning 1 value; one point is actually closer than another after machine precision arithmetic.

you'd need e.g. KSSV's answer below along with a tolerance for how many of the sorted differences are 'close enough'

you can also do something like:

[row,col ] = find( abs(difference-val)<2*eps )  

where eps is matlab's built in machine threshold

[Daniel Vazquez Pombo]

Thank you for the explanation, I will remember it in the future

Answer 1

[KSSV]

d = abs(A-b) ; 
[d,idx] = sort(d) ; % sort them in increasing order 
iwant = min(A(idx(1:2)))

You can try knnsearch...read about it.

[Daniel Vazquez Pombo]

thanks this solved my problem. Then if b is positive I needed to add this

A=[-0.1000   -0.0800   -0.0600   -0.0400   -0.0200   0   0.0200    0.0400    0.0600    0.0800    0.1000];%dummy data
b=-0.03

d = abs(A-b) ; 
[d,idx] = sort(d) ; % sort them in increasing order 
if b<0
iwant = min(A(idx(1:2)))
else
iwant = max(A(idx(1:2)))
end

I'll leave it here in case it helps someone in the future.