Reduce append

Author: itsubaki

math/matrix/matrix.go

@@ -22,9 +22,9 @@ func New(v ...[]complex128) Matrix {
 		cols = len(v[0])
 	}
 
-	data := make([]complex128, 0, rows*cols)
+	data := make([]complex128, rows*cols)
 	for i := range rows {
-		data = append(data, v[i]...)
+		copy(data[i*cols:(i+1)*cols], v[i])
 	}
 
 	return Matrix{
@@ -115,7 +115,7 @@ func (m Matrix) Transpose() Matrix {
 	out := Zero(p, q)
 	for i := range p {
 		for j := range q {
-			out.Set(i, j, m.At(j, i))
+			out.Set(j, i, m.At(i, j))
 		}
 	}
 
@@ -305,12 +305,14 @@ func (m Matrix) TensorProduct(n Matrix) Matrix {
 	p, q := m.Dimension()
 	a, b := n.Dimension()
 
-	data := make([]complex128, 0, p*a*q*b)
+	var idx int
+	data := make([]complex128, p*a*q*b)
 	for i := range p {
 		for k := range a {
 			for j := range q {
 				for l := range b {
-					data = append(data, m.At(i, j)*n.At(k, l))
+					data[idx] = m.At(i, j) * n.At(k, l)
+					idx++
 				}
 			}
 		}

math/vector/vector.go

@@ -66,10 +66,14 @@ func (v Vector) Mul(z complex128) Vector {
 
 // TensorProduct returns the tensor product of v and w.
 func (v Vector) TensorProduct(w Vector) Vector {
-	out := make(Vector, 0, len(v)*len(w))
-	for i := range v {
-		for j := range w {
-			out = append(out, v[i]*w[j])
+	p, q := len(v), len(w)
+
+	var idx int
+	out := make(Vector, p*q)
+	for i := range p {
+		for j := range q {
+			out[idx] = v[i] * w[j]
+			idx++
 		}
 	}
 
@@ -90,18 +94,21 @@ func (v Vector) InnerProduct(w Vector) complex128 {
 
 // OuterProduct returns the outer product of v and w.
 func (v Vector) OuterProduct(w Vector) matrix.Matrix {
+	p, q := len(v), len(w)
 	dual := w.Dual()
 
-	data := make([]complex128, 0, len(v))
+	var idx int
+	data := make([]complex128, p*q)
 	for i := range v {
 		for j := range dual {
-			data = append(data, v[i]*dual[j])
+			data[idx] = v[i] * dual[j]
+			idx++
 		}
 	}
 
 	return matrix.Matrix{
-		Rows: len(v),
-		Cols: len(w),
+		Rows: p,
+		Cols: q,
 		Data: data,
 	}
 }

quantum/density/matrix.go

@@ -55,9 +55,11 @@ func (m *Matrix) At(i, j int) complex128 {
 
 // Qubits returns the qubits of the density matrix.
 func (m *Matrix) Qubits() []Qubit {
-	var qubits []Qubit
-	for i := range m.NumQubits() {
-		qubits = append(qubits, Qubit(i))
+	n := m.NumQubits()
+
+	qubits := make([]Qubit, n)
+	for i := range n {
+		qubits[i] = Qubit(i)
 	}
 
 	return qubits

quantum/gate/gate.go

@@ -299,14 +299,14 @@ func QFT(n int) matrix.Matrix {
 	g := I(n)
 
 	for i := range n {
-		h := make([]matrix.Matrix, 0)
-		for j := 0; j < n; j++ {
+		h := make([]matrix.Matrix, n)
+		for j := range n {
 			if i == j {
-				h = append(h, H())
+				h[j] = H()
 				continue
 			}
 
-			h = append(h, I())
+			h[j] = I()
 		}
 
 		g = g.Apply(matrix.TensorProduct(h...))

quantum/qubit/state.go

@@ -20,9 +20,9 @@ type State struct {
 
 // NewState returns a new State.
 func NewState(amp complex128, binary ...string) State {
-	var intv []int64
-	for _, bin := range binary {
-		intv = append(intv, number.Must(strconv.ParseInt(bin, 2, 0)))
+	intv := make([]int64, len(binary))
+	for i, bin := range binary {
+		intv[i] = number.Must(strconv.ParseInt(bin, 2, 0))
 	}
 
 	return State{