LuaJIT laplace solver

laplace_cdata.lua

require 'torch'
local ffi = require("ffi")

function print_mat(mat)
   for r=1,#mat do
      row = ''
      for c=1,#mat[r] do
	 row = row .. mat[r][c] .. '\t'
      end
      print(row)
   end
end

function calc(N, Niter)
   local matrix_t = ffi.typeof("double[$][$]", N, N)
   --u = ffi.new("double[$][$]", N, N
   u = matrix_t()
   for i=0,N-1 do
      u[0][i] = 1
   end
   for i=0,Niter-1 do
      lua_update(u, N)
   end
   return u
end

function lua_update(u, N)
   local dx = 0.1
   local dy = 0.1
   local dx2 = dx*dx
   local dy2 = dy*dy

   -- Assume u is square
   ny,nx = N, N
   for i=1,nx-1 do
      for j=1,ny-1 do
	 u[i][j] = ((u[i+1][j] + u[i-1][j]) * dy2 +
		    (u[i][j+1] + u[i][j-1]) * dx2) / (2*(dx2+dy2))
      end
   end
end

timer = torch.Timer()
u = calc(100,8000)
print(timer:time().real)
print(u[1][1])