Interpolate from triangle midpoint data to node data
The geometry of the PDE problem is given by the mesh data p and t. For details on the mesh data representation, see initmesh.
Let N be the dimension of the PDE system, np the number of node points, and nt the number of triangles. The components of triangle data in ut are stored as N rows of length nt. The components of the node data are stored in un as N columns of length np.
pdeprtni and pdeintrp are not inverse functions. The interpolation introduces some averaging.