マルチグリッド法（２）

MG(IN k, INOUT x, IN b) {

if (k is the coarsest) Solve Akx = b

else {

Pkx = Qkx + b // pre-smoothing

b1 = r(b - Akx) // coarse-grid

x0 = 0 // correction

repeat (cycle) call MG(k-1, x0, b1)

x = x - px0

Pkx = Qkx + b // post-smoothing

}