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// Copyright ©2019 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.
//go:build !amd64 || noasm || gccgo || safe
// +build !amd64 noasm gccgo safe
package f64
import "math"
// L2NormUnitary returns the L2-norm of x.
func L2NormUnitary(x []float64) (norm float64) {
var scale float64
sumSquares := 1.0
for _, v := range x {
if v == 0 {
continue
}
absxi := math.Abs(v)
if math.IsNaN(absxi) {
return math.NaN()
}
if scale < absxi {
s := scale / absxi
sumSquares = 1 + sumSquares*s*s
scale = absxi
} else {
s := absxi / scale
sumSquares += s * s
}
}
if math.IsInf(scale, 1) {
return math.Inf(1)
}
return scale * math.Sqrt(sumSquares)
}
// L2NormInc returns the L2-norm of x.
func L2NormInc(x []float64, n, incX uintptr) (norm float64) {
var scale float64
sumSquares := 1.0
for ix := uintptr(0); ix < n*incX; ix += incX {
val := x[ix]
if val == 0 {
continue
}
absxi := math.Abs(val)
if math.IsNaN(absxi) {
return math.NaN()
}
if scale < absxi {
s := scale / absxi
sumSquares = 1 + sumSquares*s*s
scale = absxi
} else {
s := absxi / scale
sumSquares += s * s
}
}
if math.IsInf(scale, 1) {
return math.Inf(1)
}
return scale * math.Sqrt(sumSquares)
}
// L2DistanceUnitary returns the L2-norm of x-y.
func L2DistanceUnitary(x, y []float64) (norm float64) {
var scale float64
sumSquares := 1.0
for i, v := range x {
v -= y[i]
if v == 0 {
continue
}
absxi := math.Abs(v)
if math.IsNaN(absxi) {
return math.NaN()
}
if scale < absxi {
s := scale / absxi
sumSquares = 1 + sumSquares*s*s
scale = absxi
} else {
s := absxi / scale
sumSquares += s * s
}
}
if math.IsInf(scale, 1) {
return math.Inf(1)
}
return scale * math.Sqrt(sumSquares)
}
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