numeric vector of the same length as x or missing. Errors of the
values.
seed
integer. Seed to use for the random number generation. If it is
missing, the seed will not be set to any particular value. If there was a
default value, all results would be exactly correlated. So if you want
reproducability by fixing the seeds, make sure you choose different seeds
for independent variables.
Value
A matrix with as many columns as there are variables in x and as many rows
as boot.R.