Update density matrix

quantum/density/flip.go

@@ -0,0 +1,39 @@
+package density
+
+import (
+	"fmt"
+	"math"
+
+	"github.com/itsubaki/q/math/matrix"
+	"github.com/itsubaki/q/math/number"
+	"github.com/itsubaki/q/quantum/gate"
+)
+
+// Flip returns the flip channel.
+func Flip(p float64, m matrix.Matrix) (matrix.Matrix, matrix.Matrix, error) {
+	if p < 0 || p > 1 {
+		return nil, nil, fmt.Errorf("p must be 0 <= p =< 1. p=%v", p)
+	}
+
+	d, _ := m.Dimension()
+	n := number.Must(number.Log2(d))
+
+	e0 := gate.I(n).Mul(complex(math.Sqrt(p), 0))
+	e1 := m.Mul(complex(math.Sqrt(1-p), 0))
+	return e0, e1, nil
+}
+
+// BitFlip returns the bit flip channel.
+func BitFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
+	return Flip(p, gate.X())
+}
+
+// PhaseFlip returns the phase flip channel.
+func PhaseFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
+	return Flip(p, gate.Z())
+}
+
+// BitPhaseFlip returns the bit-phase flip channel.
+func BitPhaseFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
+	return Flip(p, gate.Y())
+}

quantum/density/flip_test.go

@@ -0,0 +1,85 @@
+package density_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/itsubaki/q/quantum/density"
+)
+
+func TestFlip(t *testing.T) {
+	cases := []struct {
+		in     float64
+		hasErr bool
+	}{
+		{-1, true},
+	}
+
+	for _, c := range cases {
+		_, _, err := density.BitPhaseFlip(c.in)
+		if (err != nil) != c.hasErr {
+			t.Errorf("err: %v", err)
+			continue
+		}
+	}
+}
+
+func ExampleBitFlip() {
+	m0, m1, _ := density.BitFlip(0.5)
+
+	for _, r := range m0 {
+		fmt.Println(r)
+	}
+	fmt.Println()
+
+	for _, r := range m1 {
+		fmt.Println(r)
+	}
+
+	// Output:
+	// [(0.7071067811865476+0i) (0+0i)]
+	// [(0+0i) (0.7071067811865476+0i)]
+	//
+	// [(0+0i) (0.7071067811865476+0i)]
+	// [(0.7071067811865476+0i) (0+0i)]
+}
+
+func ExamplePhaseFlip() {
+	m0, m1, _ := density.PhaseFlip(0.5)
+
+	for _, r := range m0 {
+		fmt.Println(r)
+	}
+	fmt.Println()
+
+	for _, r := range m1 {
+		fmt.Println(r)
+	}
+
+	// Output:
+	// [(0.7071067811865476+0i) (0+0i)]
+	// [(0+0i) (0.7071067811865476+0i)]
+	//
+	// [(0.7071067811865476+0i) (0+0i)]
+	// [(0+0i) (-0.7071067811865476+0i)]
+}
+
+func ExampleBitPhaseFlip() {
+	m0, m1, _ := density.BitPhaseFlip(0.5)
+
+	for _, r := range m0 {
+		fmt.Println(r)
+	}
+	fmt.Println()
+
+	for _, r := range m1 {
+		fmt.Println(r)
+	}
+
+	// Output:
+	// [(0.7071067811865476+0i) (0+0i)]
+	// [(0+0i) (0.7071067811865476+0i)]
+	//
+	// [(0+0i) (0-0.7071067811865476i)]
+	// [(0+0.7071067811865476i) (0+0i)]
+}

quantum/density/matrix.go

@@ -2,7 +2,6 @@ package density
 
 import (
 	"fmt"
-	"math"
 	"strconv"
 
 	"github.com/itsubaki/q/math/matrix"
@@ -17,7 +16,7 @@ type Matrix struct {
 }
 
 // New returns a new density matrix.
-func New(ensemble []State) (*Matrix, error) {
+func New(ensemble []State) *Matrix {
 	m := &Matrix{matrix.New()}
 
 	for _, s := range Normalize(ensemble) {
@@ -26,10 +25,6 @@ func New(ensemble []State) (*Matrix, error) {
 			m.m = matrix.Zero(n, n)
 		}
 
-		if len(m.m) != n {
-			return nil, fmt.Errorf("invalid dimension. m=%d n=%d", len(m.m), n)
-		}
-
 		op := s.Qubit.OuterProduct(s.Qubit).Mul(complex(s.Probability, 0))
 		for i := 0; i < n; i++ {
 			for j := 0; j < n; j++ {
@@ -38,7 +33,7 @@ func New(ensemble []State) (*Matrix, error) {
 		}
 	}
 
-	return m, nil
+	return m
 }
 
 // Raw returns the raw matrix.
@@ -139,35 +134,6 @@ func (m *Matrix) Depolarizing(p float64) (*Matrix, error) {
 	return &Matrix{i.Add(r)}, nil
 }
 
-// Flip returns the flip channel.
-func Flip(p float64, m matrix.Matrix) (matrix.Matrix, matrix.Matrix, error) {
-	if p < 0 || p > 1 {
-		return nil, nil, fmt.Errorf("p must be 0 <= p =< 1. p=%v", p)
-	}
-
-	d, _ := m.Dimension()
-	n := number.Must(number.Log2(d))
-
-	e0 := gate.I(n).Mul(complex(math.Sqrt(p), 0))
-	e1 := m.Mul(complex(math.Sqrt(1-p), 0))
-	return e0, e1, nil
-}
-
-// BitFlip returns the bit flip channel.
-func BitFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
-	return Flip(p, gate.X())
-}
-
-// PhaseFlip returns the phase flip channel.
-func PhaseFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
-	return Flip(p, gate.Z())
-}
-
-// BitPhaseFlip returns the bit-phase flip channel.
-func BitPhaseFlip(p float64) (matrix.Matrix, matrix.Matrix, error) {
-	return Flip(p, gate.Y())
-}
-
 func take(binary string, index []int) (string, string) {
 	var out, remain string
 	for i, v := range binary {