colon operator bug?

Is creating an array by saying;

x = 1:5;

not robust? Because

x(3)

returned something like

3.0001221

And I got an

Array indices must be positive integers or logical values.

error when trying to index into another array using my "x".

I can share the real script (which is pretty long) and the files (1+ GB) but wanted to ask the simpler version first. If the colon operator for sure works perfect I should probably go spend some more time before posting

[Riccardo Scorretti]

There is no reason to observe the described behaviour. By the way, I cannot reproduce:

x = 1:5;
format long ; x(3)

ans = 
     3

Are you sure there isn't something else? -- I mean, some code between the definition of x and x(3)?

Answer 1

[Can Atalay]

My bad, turns out I changed a for loop index inside that for loop and appended the index it to an array, and the index turned out not functioning like an integer somehow.

Fixed itself when I corrected the index names - we can delete the question if you guys want

Answer 2

[Jan]

The colon operator works as expected. For integer values it does reply integers. But be aware of rounding effects for floating point values:

a = 0:0.1:1
any(a == 0.3)  % FALSE!

See FAQ: Why is 0.1+0.2~=0.3

[Riccardo Scorretti]

Exact, because 0.1 is periodic in base 1. But here, it should not be the case.

[Stephen23]

"because 0.1 is periodic in base 1"

Can you please show us 0.1 written in base 1. Or any fractional number in base 1, for that matter.

"But here, it should not be the case."

Which is more likely:

• COLON has a major bug which thousands and thousands of users never noticed.
• The OP's code does not do what they think it is doing.