Heat equation - Wikipedia
https://en.wikipedia.org/wiki/Heat_equationInformally, the Laplacian operator ∆ gives the difference between the average value of a function in the neighborhood of a point, and its value at that point. Thus, if u is the temperature, ∆ tells whether (and by how much) the material surrounding each point is hotter or colder, on the average, than the material at that point. By the second law of thermodynamics, heat will flow from hotter bodies to adjacent colder bodie…