for (int j = 1; j < h + 1; j++)
{
thetaXp[i - 1, j - 1] = (thetaX[i - 1, j - 1] + 2 * thetaX[i, j - 1] + thetaX[i + 1, j - 1]
+ 2 * thetaX[i - 1, j] + 4 * thetaX[i, j] + 2 * thetaX[i + 1, j]
+ thetaX[i - 1, j + 1] + 2 * thetaX[i, j + 1] + thetaX[i + 1, j + 1]) / 16f;
{
thetaXp[i - 1, j - 1] = (thetaX[i - 1, j - 1] + 2 * thetaX[i, j - 1] + thetaX[i + 1, j - 1]
+ 2 * thetaX[i - 1, j] + 4 * thetaX[i, j] + 2 * thetaX[i + 1, j]
+ thetaX[i - 1, j + 1] + 2 * thetaX[i, j + 1] + thetaX[i + 1, j + 1]) / 16f;