Maths Course - Rounding - incorrect Calcs?

[EddieRocks]

At 4.34 ish

void Start()
{
float a = 5.3f;
float b = 4.7f;
float c = 2.5f;

    print(a * b + c);
    print(Mathf.Round(a) + "  " +  Mathf.Round(b) + "  " + Mathf.Round(c));
    print(Mathf.Round(a) * Mathf.Round(b) + Mathf.Round(c));
}

gave me
27.41
5 5 2
27

not in the vid which had 26.47 and 28

[garypettie]

Thanks for pointing this out @EddieRocks, you’re absolutely right - I really should have noticed that before the video got uploaded and will get it corrected asap. I’ll also do everything I can to stop it happening again.

The correct sum should have been:
5.1 x 4.7 + 2.5 = 26.47
This then rounds down to 26.

Rather than:
5.3 x 4.7 + 2.5 = 27.41, as you said.

The second half is correct though (using traditional rounding), as 2.5 would round up to 3, so;
5 x 5 + 3 = 25 + 3 = 28

The System.Math library in C# actually uses banker’s rounding by default, so by extension UnityEngine.Mathf does too. This is the same in some other languages too, but not all.

This means that if a number is equidistant between two integers (i.e. x.5), the nearest even integer is returned - so if x is even then the 0.5 is rounded down and if x is odd then it gets rounded up.
For example, 2.5 would round down to 2 and 3.5 would round up to 4.

This might sound kind of weird but it does have it’s uses, especially when you’re dealing with a lot of numbers that need rounding.

In some Round functions you can pass in a second parameter to specify the type of midpoint rounding you want to use. However, in Unity, Mathf.Round doesn’t let you do this.
One way around it would be to use the System.Math library directly and write something like;
System.Math.Round(x, System.MidpointRounding.AwayFromZero);
(You can remove the System part if you include using System; at the top of your script)

I’m trying to keep examples in pseudo-code rather than being language specific, but noting some of these weird quirks could definitely be helpful. My main advice though would be to always check the docs when using a new function for the first time, as they don’t always work like you’d expect.

Anyway, I hope that all helps.
I really want to make the course the best it can be, so any feedback (good or bad) is very much appreciated - and definitely continue to call me out if/when I make mistakes!

[Kevin-Brandon]

You are doing a great job Gary! New video with correct values is uploaded

[EddieRocks]

Thanks Gary.

Very interesting on the actual rounding - I’d not heard of bankers rounding even though I did work for a bank though it makes a little sense in averaging out things though doubt it has been used in banks for many many years .
Also lucky you chose an even number or I wouldn’t have known any better.

I am hoping the course though maths, is focused around uses in gaming/coding which most of the course so far has been lacking…