From c02b01b23d7eb5283e8f9afea0c4644da1b740a7 Mon Sep 17 00:00:00 2001
From: Christoph Ruegg <git@cdrnet.ch>
Date: Sun, 27 Jun 2021 15:42:07 +0200
Subject: [PATCH] Expose previously internal Series.Evaluate

---
 build.fsx                                  |   2 +-
 src/Numerics/Series.cs                     | 106 +++++++++++++++++++++
 src/Numerics/SpecialFunctions/Evaluate.cs  |  31 +-----
 src/Numerics/SpecialFunctions/Stability.cs |   2 +-
 4 files changed, 109 insertions(+), 32 deletions(-)
 create mode 100644 src/Numerics/Series.cs

diff --git a/build.fsx b/build.fsx
index c4c0259d..6d78b463 100644
--- a/build.fsx
+++ b/build.fsx
@@ -385,7 +385,7 @@ Target "DocsWatch" (fun _ ->
 Target "CleanApi" (fun _ -> CleanDirs ["out/api"])
 
 Target "Api" (fun _ ->
-    !! "src/Numerics/bin/Release/net40/MathNet.Numerics.dll"
+    !! "src/Numerics/bin/Release/net461/MathNet.Numerics.dll"
     |> Docu (fun p ->
         { p with
             ToolPath = "tools/docu/docu.exe"
diff --git a/src/Numerics/Series.cs b/src/Numerics/Series.cs
new file mode 100644
index 00000000..77e2c3ee
--- /dev/null
+++ b/src/Numerics/Series.cs
@@ -0,0 +1,106 @@
+// <copyright file="Series.cs" company="Math.NET">
+// Math.NET Numerics, part of the Math.NET Project
+// https://numerics.mathdotnet.com
+// https://github.com/mathnet/mathnet-numerics
+//
+// Copyright (c) 2009-2021 Math.NET
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+
+namespace MathNet.Numerics
+{
+    public static class Series
+    {
+        /// <summary>
+        /// Numerically stable series summation (stops automatically).
+        /// </summary>
+        /// <param name="nextSummand">provides the summands sequentially</param>
+        /// <returns>Sum</returns>
+        public static double Evaluate(Func<double> nextSummand)
+        {
+            double compensation = 0.0;
+            double current;
+            const double factor = 1 << 16;
+
+            double sum = nextSummand();
+
+            do
+            {
+                // Kahan Summation
+                // NOTE (ruegg): do NOT optimize. Now, how to tell that the compiler?
+                current = nextSummand();
+                double y = current - compensation;
+                double t = sum + y;
+                compensation = t - sum;
+                compensation -= y;
+                sum = t;
+            }
+            while (Math.Abs(sum) < Math.Abs(factor*current));
+
+            return sum;
+        }
+
+        /// <summary>
+        /// Numerically stable series summation (stops automatically).
+        /// </summary>
+        /// <param name="infiniteSummands">provides the summands sequentially</param>
+        /// <returns>Sum</returns>
+        public static double Evaluate(IEnumerable<double> infiniteSummands)
+        {
+            double compensation = 0.0;
+            double current, sum;
+            const double factor = 1 << 16;
+
+            using (var enumerator = infiniteSummands.GetEnumerator())
+            {
+                if (!enumerator.MoveNext())
+                {
+                    return 0.0;
+                }
+
+                sum = enumerator.Current;
+                if (!enumerator.MoveNext())
+                {
+                    return sum;
+                }
+
+                do
+                {
+                    // Kahan Summation
+                    // NOTE (ruegg): do NOT optimize. Now, how to tell that the compiler?
+                    current = enumerator.Current;
+                    double y = current - compensation;
+                    double t = sum + y;
+                    compensation = t - sum;
+                    compensation -= y;
+                    sum = t;
+                } while (Math.Abs(sum) < Math.Abs(factor * current) && enumerator.MoveNext());
+            }
+
+            return sum;
+        }
+    }
+}
diff --git a/src/Numerics/SpecialFunctions/Evaluate.cs b/src/Numerics/SpecialFunctions/Evaluate.cs
index 4df41602..7ea5d5ff 100644
--- a/src/Numerics/SpecialFunctions/Evaluate.cs
+++ b/src/Numerics/SpecialFunctions/Evaluate.cs
@@ -52,37 +52,8 @@ namespace MathNet.Numerics
     /// <summary>
     /// Evaluation functions, useful for function approximation.
     /// </summary>
-    public static class Evaluate
+    internal static class Evaluate
     {
-        /// <summary>
-        /// Numerically stable series summation
-        /// </summary>
-        /// <param name="nextSummand">provides the summands sequentially</param>
-        /// <returns>Sum</returns>
-        internal static double Series(Func<double> nextSummand)
-        {
-            double compensation = 0.0;
-            double current;
-            const double factor = 1 << 16;
-
-            double sum = nextSummand();
-
-            do
-            {
-                // Kahan Summation
-                // NOTE (ruegg): do NOT optimize. Now, how to tell that the compiler?
-                current = nextSummand();
-                double y = current - compensation;
-                double t = sum + y;
-                compensation = t - sum;
-                compensation -= y;
-                sum = t;
-            }
-            while (Math.Abs(sum) < Math.Abs(factor*current));
-
-            return sum;
-        }
-
         /// <summary> Evaluates the series of Chebyshev polynomials Ti at argument x/2.
         /// The series is given by
         /// <pre>
diff --git a/src/Numerics/SpecialFunctions/Stability.cs b/src/Numerics/SpecialFunctions/Stability.cs
index 3758e0f1..82f99971 100644
--- a/src/Numerics/SpecialFunctions/Stability.cs
+++ b/src/Numerics/SpecialFunctions/Stability.cs
@@ -56,7 +56,7 @@ namespace MathNet.Numerics
             // Series Expansion to x^k / k!
             int k = 0;
             double term = 1.0;
-            return Evaluate.Series(
+            return Series.Evaluate(
                 () =>
                 {
                     k++;