ftcurvpi calculates an integral of an interpolatory spline between two specified points. ftcurvpi is in the Fitgrid package -- a package containing 1D and 2D interpolators using cubic splines under tension.
function ftcurvpi( xl[1] : float, xr[1] : float, p[1] : float, xi[*] : float, yi[*] : float )
The only control parameter that applies to ftcurvpi is: sig.
The value for the parameter sig specifies the tension factor. Values near zero result in a cubic spline; large values (e.g. 50) result in nearly a polygonal line. A typical value is 1. (the default).
You can extrapolate values with ftcurvpi (that is calculate interpolated values for abscissae outside of the domain of the input), but these values are, in general, unreliable.
begin xi = (/ 0.00, 2.00, 5.00, 8.00, 10.00, 13.00, \ 15.00, 18.00, 21.00, 23.00, 30.00 /) yi = (/ 1.00, 0.81, 0.00, -0.81, -1.00, -0.84, \ -0.56, 0.04, 0.73, 1.18, 2.0 /) npts = 201 xo = fspan(0.,35.,npts) integral = ftcurvpi(10., 30., 31., xi, yi) end
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