added first test case for general nevile

interp.go

@@ -2,6 +2,7 @@ package govector
 
 import (
 	"errors"
+	"fmt"
 )
 
 // explicitly implements Neville's algorithm for three points at very
@@ -21,3 +22,16 @@ func Extrapolate(P []Point2d) (*Point2d, error) {
 	p012 := p01.ToVector().Scale(-1.0 / 2.0).ToPoint().Add(p12.ToVector().Scale(3.0 / 2.0))
 	return &p012, nil
 }
+
+func Neville(P []Point2d, ts []float64, t float64) (*Point2d, error) {
+	if len(P) != len(ts) {
+		return nil, errors.New(
+			fmt.Sprintf(
+				"Incompatable slice lengths len(P): %d != len(ts): %d",
+				len(P),
+				len(ts),
+			),
+		)
+	}
+	return nil, errors.New("smb")
+}