functions:interpolation:INTERP
syntax: INTERP( x, y, xout )
INTERP( x, y, xout, `SPLINE' )
The interpolant is calculated by the method of cubic splines under
tension. The tension corresponds to the curviness, and must be > 0.
If it is close to 0, each interpolated function is almost a cubic
spline and the resulting curve is quite loose. If it is large, then
the interpolation is almost linear. The tension used is the current
value of TENSION, which may be changed with the SET command.
syntax: INTERP( x, y, xout, `FC' )
The interpolated values are calculated using the Fritsch and Carlson
method of monotone piecewise cubic interpolation.
syntax: INTERP( x, y, xout, `LINEAR' )
The interpolating method used is linear interpolation.
syntax: INTERP( x, y, xout, `LAGRANGE' )
The interpolating method used is general Lagrange interpolation. The
degree of the interpolating polynomial depends on the number of input
data points. Suppose that n is the number of points specified by the
dimensions of x and y. If n=2, then a simple straight line is used
for interpolating. If n=3 or n=4, then a quadratic is used. If n>=5,
then a polynomial of degree 4 is used for the interpolation.