Add improvements to pwl

Author: marcin-golebiowski

SpiceSharpBehavioral/Builders/Functions.cs

@@ -293,6 +293,16 @@ public static double RampDerivative(double arg)
         /// <returns>The interpolated value.</returns>
         public static double Pwl(double arg, Point[] data)
         {
+            if (arg <= data[0].X)
+            {
+                return data[0].Y;
+            }
+
+            if (arg >= data[data.Length - 1].X)
+            {
+                return data[data.Length - 1].Y;
+            }
+
             // Narrow in on the index for the piece-wise linear function
             int k0 = 0, k1 = data.Length;
             while (k1 - k0 > 1)
@@ -314,6 +324,11 @@ public static double Pwl(double arg, Point[] data)
         /// <returns>The interpolated value.</returns>
         public static double PwlDerivative(double arg, Point[] data)
         {
+            if (arg <= data[0].X || arg >= data[data.Length - 1].X)
+            {
+                return 0.0;
+            }
+
             // Narrow in on the index for the piece-wise linear function
             int k0 = 0, k1 = data.Length;
             while (k1 - k0 > 1)

SpiceSharpBehavioralTest/Builders/BuilderTestData.cs

@@ -57,6 +57,8 @@ public static IEnumerable<TestCaseData> FunctionNodes
                 yield return new TestCaseData(Node.Function("abs", Node.Add(Node.Multiply(Node.Minus(2.0), 6.0), 7.0)), 5.0).SetName("{m}(abs -2*6+7)");
                 yield return new TestCaseData(Node.Function("min", Node.Minus(2.0), Node.Multiply(6.0, 2.0)), -2.0).SetName("{m}(min -2, 6*2)");
                 yield return new TestCaseData(Node.Function("pwl", 2.0, 0.0, 1.0, 3.0, 4.0), 3.0).SetName("{m}(pwl 2,0,1,3,4)");
+                yield return new TestCaseData(Node.Function("pwl", -1.0, 0.0, 1.0, 3.0, 4.0), 1.0).SetName("{m}(pwl -1,0,1,3,4)");
+                yield return new TestCaseData(Node.Function("pwl", 4.0, 0.0, 1.0, 3.0, 4.0), 4.0).SetName("{m}(pwl 4,0,1,3,4)");
                 yield return new TestCaseData(Node.Function("table", 2.0, 0.0, 1.0, 3.0, 4.0), 3.0).SetName("{m}(table 2,0,1,3,4)");
                 yield return new TestCaseData(Node.Function("tbl", 2.0, 0.0, 1.0, 3.0, 4.0), 3.0).SetName("{m}(tbl 2,0,1,3,4)");
                 yield return new TestCaseData(Node.Function("if", 1.0, 0.25, 0.75), 0.25).SetName("{m}(if 1 0.25 0.75)");