1 files changed, 53 insertions, 0 deletions
diff --git a/mstep/common.go b/mstep/common.go
new file mode 100644
index 0000000..2ecff09
--- /dev/null
+++ b/mstep/common.go
@@ -0,0 +1,53 @@
+// Common code to define stepping methods.
+//
+// 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
+
+type Step struct {
+	Value []float64
+	Deriv []float64
+}
+
+func Implicit(steps []Step, a []float64, b []float64, step float64) []float64 {
+	if len(steps) == 0 {
+		panic("There must be at least one step!\n")
+	}
+	if len(steps) < len(a) || len(steps) < len(b) {
+		panic("There must be at least as many steps as coefficients.\n")
+	}
+
+	result := make([]float64, len(steps[0].Value))
+	for i, v := range a {
+		for j := range result {
+			result[j] += v * steps[i].Value[j]
+		}
+	}
+	for i, v := range b {
+		for j := range result {
+			result[j] += step * v * steps[i].Deriv[j]
+		}
+	}
+	return result
+}
+
+func Shift(steps []Step) {
+	for i := len(steps) - 1; i > 0; i-- {
+		steps[i] = steps[i-1]
+	}
+}