added first test case for general nevile

.gitignore

@@ -1 +1,2 @@
 tags
+.*.swp

govector_test.go

@@ -1,6 +1,7 @@
 package govector
 
 import (
+	"errors"
 	"math"
 	"testing"
 )
@@ -648,3 +649,67 @@ func TestExtrapolate(t *testing.T) {
 		}
 	}
 }
+
+func TestNeville(t *testing.T) {
+	knownFails := []struct {
+		points   []Point2d
+		ts       []float64
+		t        float64
+		expected Point2d
+		err      error
+	}{
+		{
+			points: []Point2d{
+				{0, 0},
+				{1, 1},
+				{2, 2},
+			},
+			ts: []float64{
+				1.0 / 3.0,
+				2.0 / 3.0,
+			},
+			err: errors.New("Incompatable slice lengths len(P): 3 != len(ts): 2"),
+		},
+	}
+	for _, test := range knownFails {
+		p, err := Neville(test.points, test.ts, test.t)
+		if p != nil {
+			t.Errorf("p should've been nil: %+v", p)
+
+		}
+		if err.Error() != test.err.Error() {
+			t.Errorf("expected err: '%s', unexpectd err: '%s'", test.err, err)
+		}
+	}
+	tests := []struct {
+		points   []Point2d
+		ts       []float64
+		t        float64
+		expected Point2d
+	}{
+		{
+			points: []Point2d{
+				{0, 0},
+				{1, 1},
+				{2, 2},
+			},
+			ts: []float64{
+				0.0,
+				1.0 / 3.0,
+				2.0 / 3.0,
+			},
+			t:        1.0,
+			expected: Point2d{3, 3},
+		},
+	}
+	for _, test := range tests {
+		p, err := Neville(test.points, test.ts, test.t)
+		if err != nil {
+			t.Errorf("yeah, this should've been nil: %s", err)
+		}
+		if p == nil {
+		} else if *p != test.expected {
+			t.Errorf("wrong: expected: %+v, actual: %+v", test.expected, p)
+		}
+	}
+}

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")
+}