MATLAB: Ismembertol does not work as documented

ismembertol

Hello,
This function should work with absolute tolerance. Here is an example where it doesn't work as documented
B=[ 1.9500    1.0000];
A=[3.0000    2.0000    4.0000    2.5000    1.2000    1.1000];
[Loc1,Loc2]=ismembertol(B,A,0.1,'DataScale',1)
What should come out according to documentation is 
Loc1 =
  1×2 logical array
   1   1
Loc2 =
     2     6
What does come out however is 
Loc1 =
  1×2 logical array
   1   0
Loc2 =
     2     0
It seems someone forgot the absolute when comparing 🙂

Best Answer

The documentation isn't wrong. You've set a tolerance that can only satisfied reliably at A(6) in infinite precision arithmetic. Observe:
>> [Loc1,Loc2]=ismembertol(B,A,0.1+eps,'DataScale',1)
Loc1 =
  1×2 logical array
   1   1
Loc2 =
     2     6
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