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 // Copyright ©2016 The Gonum Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package integrate import ( "math" "testing" "gonum.org/v1/gonum/floats" ) func TestTrapezoidal(t *testing.T) { const N = 1e6 x := floats.Span(make([]float64, N), 0, 1) for i, test := range []struct { x []float64 f func(x float64) float64 want float64 }{ { x: x, f: func(x float64) float64 { return x }, want: 0.5, }, { x: floats.Span(make([]float64, N), -1, 1), f: func(x float64) float64 { return x }, want: 0, }, { x: x, f: func(x float64) float64 { return x + 10 }, want: 10.5, }, { x: x, f: func(x float64) float64 { return 3*x*x + 10 }, want: 11, }, { x: x, f: func(x float64) float64 { return math.Exp(x) }, want: 1.7182818284591876, }, { x: floats.Span(make([]float64, N), 0, math.Pi), f: func(x float64) float64 { return math.Cos(x) }, want: 0, }, { x: floats.Span(make([]float64, N), 0, 2*math.Pi), f: func(x float64) float64 { return math.Cos(x) }, want: 0, }, { x: floats.Span(make([]float64, N*10), 0, math.Pi), f: func(x float64) float64 { return math.Sin(x) }, want: 2, }, { x: floats.Span(make([]float64, N*10), 0, 0.5*math.Pi), f: func(x float64) float64 { return math.Sin(x) }, want: 1, }, { x: floats.Span(make([]float64, N), 0, 2*math.Pi), f: func(x float64) float64 { return math.Sin(x) }, want: 0, }, } { y := make([]float64, len(test.x)) for i, v := range test.x { y[i] = test.f(v) } v := Trapezoidal(test.x, y) if !floats.EqualWithinAbs(v, test.want, 1e-12) { t.Errorf("test #%d: got=%v want=%v\n", i, v, test.want) } } }