Factorial and Binomial Coefficient as Big Integer
Efficiently compute the factorial n! or a binomial coefficient
choose(n, k) as big integer (class bigz).
factorialZ(n) chooseZ(n, k)
n |
non-negative integer (vector), for
|
k |
non-negative integer vector. |
a vector of big integers, i.e., of class bigz.
factorialZ(0:10)# 1 1 2 6 ... 3628800 factorialZ(0:40)# larger factorialZ(200) n <- 1000 f1000 <- factorialZ(n) stopifnot(1e-15 > abs(as.numeric(1 - lfactorial(n)/log(f1000)))) system.time(replicate(8, f1e4 <<- factorialZ(10000))) nchar(as.character(f1e4))# 35660 ... (too many to even look at ..) chooseZ(1000, 100:102)# vectorizes chooseZ(as.bigz(2)^120, 10) n <- c(50,80,100) k <- c(20,30,40) ## currently with an undesirable warning: % from methods/src/eval.c _FIXME_ stopifnot(chooseZ(n,k) == factorialZ(n) / (factorialZ(k)*factorialZ(n-k)))
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