What's the algorithm behind the laplacian smooth modifier?

When I try out the laplacian smooth modifier, I noticed that if I import an open surface, the laplacian smooth modifier works on the open surface. I am wondering what is the algorithm behind it and if there is any documentation explaining the algorithm because when I tried laplacian from libigl, it doesn’t work on open surfaces, so I am just wondering if there is any difference between them. Thank you!