How do you write -0 in an array on matlab?

I have recently been tasked with sorting a variety of numerical values and Nan's using a shell sort function. It works so far but whenever I want to sort -0 it always comes out as 0 in the sorted list. Any ideas?

This is the full question: Give the output of a program run that proves it can generates minus zero as a floating-point object that is not identical to zero.

Answer 1

[Stephen23]

Note that according to standard definitions minus zero has the same value as positive zero: "...regarded as equal by the numerical comparison operations". This means they cannot be sorted (which by definition requires a value comparison function to provide the order):

>> -0<0
ans =
     0

So sort will not work for you:

>> [out,idx] = sort([0,-0])
out =
     0     0
idx =
     1     2

If you want to sort them separately you will need to implement your own sort algorithm. The most reliable way to test for minus zero is to use a divide-by-zero and check the Inf sign:

>> 1./[-0,0]
ans =
  -Inf   Inf

Note that negative zero is not displayed in MATLAB:

>> x = 1*(-0)
x =
     0
>> 1/x
ans =
  -Inf

Interestingly the sort example above keeps the negative zero in the output:

>> 1./out
ans =
   Inf  -Inf

[Alfie Sargent]

Hmmmm...i might have to use a different program for this then. It is also being very frustrating when i try to sort NaN's, it seems to work fine with one NaN but whenever I introduce two or more the sort simply doesn't work. I think i can get around the -0 problem with the above solution but it seems to be getting progressively worse.

[Guillaume]

Sorting NaN (Not a Number!) is an antinomy. By definition, there's no ordering on NaN.

If you come across a program that sorts NaN, then that program is not working properly.

[Walter Roberson]

The sort routine counts nan, removes them, sorts, adds nan to an end. It does not keep track of which nan (there are many many representations of nan), just slams in standard nan.

Answer 2

[Walter Roberson]

num2hex distinguishes +0 from -0