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Manuscript Title: A bicubic spline interpolation of unequally spaced data.
Authors: M.A. Christie, K.J.M. Moriarty
Program title: BISPLN
Catalogue identifier: ACZG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 17(1979)357
Programming language: Fortran.
Computer: CDC 6600.
Operating system: CDC SCOPE.
RAM: 5.4K words
Word size: 60
Keywords: General purpose, Interpolation, Spline, Bicubic spline, Best approximation, De boor's method.
Classification: 4.10.

Nature of problem:
A theorist may wish to interpolate data known to be a function of two variables. Often the data are not known on a regular grid, but are distributed irregularly. The 'best approximation' when interpolating data which can be assumed to be error free is with the bicubic spline method. Method of solution: We use de Boor's method and one dimensional cubic spline interpolation to calculate the coefficients of the spline in the rectangle [xi,xi+1] X [yj,yj+1]. We can then obtain an interpolated value for the function and its first derivatives.

Restrictions:
The number of x-data points must be less than 25 and the number of y- data points must be less than 10. These values can be changed by the user. The point (x,y) at which an interpolated value for the function is required must always lie in the rectangle [x1,xn] X [y1,ym]. The program makes no restrictions on the spacing of the data points on the x and y axes.

Running time:
The test run output took about 4.4 s.