Can someone explain the Math.ulp(double) method?

Question

I haven't been able to find any information online that doesn't already assume I know things. I wonder if anyone knows any good resources that I can look into to help me wrap my head around what this function does exactly?

From what I gather, and I'm pretty certain this is wrong or at least not fully right, is that given a floating point, it determines the distance between itself and some number next in a sequence? There appears to be something to do with how number are represented bitwise, but the sources I've read never explicitly said anything about that.

Answer 1

http://matlabgeeks.com/tips-tutorials/floating-point-comparisons-in-matlab/

illustrated it rather well:

float2bin(A)

//ans = 0011111110111001100110011001100110011001100110011001100110100000

float2bin(B)

//ans = 0011111110111001100110011001100110011001100110011001100110011010

You can see the difference in precision at a binary level in this example. A and B differ by 6 ulps (units in the last place)