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shadyelsayed
3,049 PointsWhy not Math.round?
I used Math.round(Math,random()*6); and I got the same result is there a reason why this could be wrong?
3 Answers
eck
43,038 PointsAll you really need to know is that Math.round rounds to the nearest integer, Math.floor always rounds down, and Math.ceil will always round up. Which one you want to use really depends on the circumstance.
ex:
Math.round(5.6); // returns 6
Math.floor(5.6); // returns 5
Math.ceil(5.6); // returns 6
dominique
2,178 PointsIn our case of a die, random means that each outcome has an equal probability of occurring. This means that each outcome (whether we get 1, 2, 3, … , 6) has a 1/6 probability of occurrence.
We have an algorithm that gives a random real number (with a certain precision) in the interval [0, 1). Multiplying each number by 6 gives us a new interval [0, 6) of random numbers.
We can break this interval into six equal-length intervals (each of length 1). Now we need to map these six intervals to the integers 1 - 6. This way, our algorithm will remain random.
Therefore, we have to create a function that will map the interval [0, 1) to the integer 1, the interval [1,2) to the integer 2.... the interval [5, 6) to the integer 6. This way, each outcome will have a 1/6 chance of occurring, and remain random.
Using Math.round will rearrange which intervals are being mapped into the integers. It will also add an interval (for a total of 7 intervals). Two of these intervals [0, 0.5) & [5.5, 6.0) will be half the length of the others. This means that the integers they map to (0 & 6, respectively) will have a 1/12 probability of occurrence. Also, we don't want to map to 0, because that is not an option on a die.
Hugo da Silva Ribas
7,666 PointsIt could hit 7.
(0.98 * 6 ) + 1 would hit up to 7 if you round up.
Hugo da Silva Ribas
7,666 PointsOh, you don't need the + 1 then...
Good question, i guees it's like dominique sad.
shadyelsayed
3,049 Pointsshadyelsayed
3,049 PointsThanks Erik, would you recommend using Math.round since it is the mathematically correct method to round up numbers i.e. since 0.1-0.4 = 0 and 0.5 to 0.9 = 1?
eck
43,038 Pointseck
43,038 PointsAgain, it kinda depends. Say I wanted a random number between 1 and 5. I could write Math.round(Math.random()*5) but if the random number is 0.1234 then it will be rounded to 0, which I didn`t want. To get my desired result, I would want to use Math.ceil(Math.random()*5) so the number is always rounded up.
There are other ways I could achieve a random number between 1 and 5, but that is just a little sample of how one rounding method could be a better choice than another in certain situations.