Hello,
My question is specific to the following section of the documentation:
Specify Absolute Tolerance
By default, ismembertol uses a tolerance test of the form abs(u-v) <= tol*DS, where DS automatically scales based on the magnitude of the input data. You can specify a different DS value to use with the DataScale option. However, absolute tolerances (where DS is a scalar) do not scale based on the magnitude of the input data.
First, compare two small values that are a distance eps apart. Specify tol and DS to make the within tolerance equation abs(u-v) <= 10^-6.
x = 0.1;
ismembertol(x, exp(log(x)), 10^-6, 'DataScale', 1)
ans =
So by the above example in the documentation, ismembertol will place a non-strict inequality for the tolerance. However, I am seeing that it is placing strict inequality when I run it on my MATLAB R2015a. Here is a simple example where I noticed it:
x = 3.8557;
y = 3.8556;
tol = 0.0001;
DS = 1;
since abs(x-y) is 0.0001, which is equal to tol*DS = 0.0001, abs(x-y)<=tol*DS is satisfied, so x should be a member of y, therefore I expect the answer to be 1.
But this is what I get:
ismembertol(x, y, tol, 'DataScale', DS)
ans =
However, when I increase tolerance by a tiny bit,
tol = 0.00011
ismembertol(x, y, tol, 'DataScale', DS)
ans =
Now it indicates that x is a member of y.
This is very confusing to me... is this a precision issue where abs(x-y) and tol are both 0.0001 yet MATLAB can't recognize that they are equal?
Any help will be greatly appreciated! Thanks in advance,
