Tuesday, August 21, 2012

Modular Dice

I've been using "d50"s without noticing for some time. You can get huge, strange 50-sided dice, but that's not what I'm talking about. Instead, I roll d% and if the tens-place is greater than 5, I "wrap around". I'm sure this is something that's not uncommon, it saves re-rolling if the die is an even multiple.

I decided to investigate this further. For a uniform distribution it's not that interesting, but starting from a normal distribution it's a neat way to get two peaks. Figure 1 shows the effects of different moduli on the 3d6 distribution.

Figure 1
If you'd like to play with this in anydice here's the function I've written:
function: A:n mod B:n {
    if A > B {result: [(A - B) mod B]}
    result: A

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