2-D biharmonic data interpolation and gridding.

  ZI = INTERP3(X,Y,Z,XI,YI) uses biharmonic interpolation to

  find ZI, the values of the underlying 2-D function in Z at the points

  in matrices XI and YI.  Matrices X and Y specify the points at which 

  the data Z is given.  X and Y can also be vectors specifying the 

  abscissae for the matrix Z as for MESHGRID1Y7VXN8. In both cases, X

  and Y must be equally spaced and monotonic.



  If X, Y, and Z are all vectors, INTERP3 interpolates within the

  data given by the (possibly irregularly spaced) ordered triplets

  (X,Y,Z) to return matrix ZI.



  ZI = INTERP3(Z,M,N) returns an M-by-N matrix ZI whose values

  are interpolated within matrix Z.



  [ZI,WEIGHTS]=INTERP3(X,Y,Z,XI,YI) also returns the computed

  interpolation WEIGHTS, which can be reused as follows:

  INTERP3(X,Y,Z,XI,YI,WEIGHTS) uses the given WEIGHTS vector,

  instead of recalculating them from X, Y, and Z.



  INTERP42DAUZYE and INTERP51R8J1B5 are much faster than INTERP3 for

  data interpolation and should be used unless irregularly

  spaced vector triplet gridding is required.