From 46afb6bf501f4001c4bdb7bd2f2db7c466f95554 Mon Sep 17 00:00:00 2001
From: Juan Marin Noguera <juan@mnpi.eu>
Date: Tue, 25 Jul 2023 18:22:04 +0200
Subject: Solvned project from 2020

Note that Go didn't have generics back then.
---
 mstep/root.go | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 mstep/root.go

(limited to 'mstep/root.go')

diff --git a/mstep/root.go b/mstep/root.go
new file mode 100644
index 0000000..20758f1
--- /dev/null
+++ b/mstep/root.go
@@ -0,0 +1,71 @@
+// Root-finding algorithms.
+//
+// Copyright (C) 2020 Juan Marín Noguera
+//
+// This file is part of Solvned.
+//
+// Solvned is free software: you can redistribute it and/or modify it under the
+// terms of the GNU Lesser General Public License as published by the Free
+// Software Foundation, either version 3 of the License, or (at your option) any 
+// later version.
+//
+// Solvned is distributed in the hope that it will be useful, but WITHOUT ANY 
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+// A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+// details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with Solvned. If not, see <https://www.gnu.org/licenses/>.
+
+package mstep
+
+import "math"
+
+func NewtonRoot1D(
+	x0, tolerance float64, f, df func(float64) (float64, bool),
+) (float64, bool) {
+	prev := x0
+	for {
+		fprev, ok := f(prev)
+		if !ok {
+			return 0, false
+		}
+		dfprev, ok := df(prev)
+		if !ok {
+			return 0, false
+		}
+		off := fprev / dfprev
+		next := prev - off
+		if math.Abs(off) <= tolerance {
+			return next, true
+		}
+		prev = next
+	}
+}
+
+func SecantRoot1D(
+	x0, x1, tolerance float64, f func(float64) (float64, bool),
+) (float64, bool) {
+	prev := x0
+	fprev, ok := f(prev)
+	if !ok {
+		return 0, false
+	}
+	cur := x1
+	fcur, ok := f(cur)
+	if !ok {
+		return 0, false
+	}
+	for {
+		off := fcur * (prev - cur) / (fprev - fcur)
+		next := cur - off
+		if math.Abs(off) <= tolerance {
+			return next, true
+		}
+		fnext, ok := f(next)
+		if !ok {
+			return 0, false
+		}
+		prev, fprev, cur, fcur = cur, fcur, next, fnext
+	}
+}
-- 
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