我想在model.matrix中插入两个变量，但我不知道该怎么做
long long factors(int N) {
long long ans = 0; // Result to return
int nr = (int) sqrt(N); // Highest possible value of the lower factor
// Count factorisations (a,b) with a ∈ 2..√N
for (int b = 2; b <= nr; b++) {
if (N % b == 0) { // If b | N ..
ans += N/b - 1; // .. then b*(N/b) = N, so count 1..(N/b - 1)
} else {
ans += N/b; // .. count 1..N/b
}
}
// Remaing steps of algorithm, optimised:
// - Add N-1 for 1st column (1,1..(N-1)), giving total (a,b) with a ∈ 1..√N
// - Double, to cover the reversed pairs (b,a) with a ∈ 1..√N, b ∈ √N..N
// - Subtract nr² or nr²-1, for pairs counted twice
int fix = N - nr * nr - 1; // A correcting term, chosen to compare to 0
if ( fix < 0) { // I.e. if nr² = N ..
ans = (2*ans) + N + fix; // .. ans = 2*(ans + N-1) - (nr² - 1)
} else {
ans = (2*ans) + N + fix - 1; // .. ans = 2*(ans + N-1) - (nr²)
}
return ans;
}
[1] 475 28
> k<-model.matrix(m2)
> dim(k)