2-D data interpolation (table lookup).

  ZI = INTERP2(X,Y,Z,XI,YI) returns matrix ZI containing elements

  corresponding to the elements of XI and YI and determined by 

  interpolation within the 2-D function described by matrices X, Y, 

  and Z.  Out of range values are returned as NaN.



  X can be a row vector, in which case the elements are assumed to 

  apply to the columns of Z. Similarly, Y can be a column vector

  and its elements are assumed to apply across the rows of Z.



  Interpolation is the same operation as "table lookup".  Described in

  "table lookup" terms, the "table" is TAB = [NaN,Y; X,Z] and INTERP2 

  "looks-up" the elements of XI in X, YI in Y, and, based upon their 

  location, returns values ZI interpolated within the elements of Z.



  By default, INTERP2 uses bilinear interpolation.

  ZI = INTERP2(X,Y,Z,XI,YI,'method') specifies alternate methods.

  Available methods are:



    'linear' - bilinear interpolation

    'cubic'  - bicubic interpolation



  All the interpolation methods require that X and Y be monotonic.

  The 'cubic' method also requires that the points in X and Y be