RStudio实验

参考：https://ocw.mit.edu/courses/mathematics/18-05-introduction-to-probability-and-statistics-spring-2014/readings/r-tut1b.html

# Goal: estimate the probability of getting a sum
# of 7 when rolling two dice.
1. > ntrials = 10000
2. > x = matrix(sample(1:6, 2*ntrials, replace=TRUE), nrow=2, ncol=ntrials)
3. > y = colSums(x)
4. > mean(y == 7)
[1] 0.1658

# Command 1: We assign the number of trials to the variable ntrials. Writing code
#       like this makes it easier to modify later. If we want to change the number 
#       of trials to 7 we just have to change this one line of code.
# Command 2: we create 10000 columns with 2 rows. That is, we run 10000 experiments 
#       of rolling 2 dice.
# Command 3: we sum each of the columns, i.e., we sum the two dice.
# Command 4: we find the fraction of sums that are 7.

# Note, this is essentially the exact answer of 1/6.