Check-in commons-math 3.6.1 am: 1354beaf45 am: 0018f64b87 am: b3715644fb

Original change: https://android-review.googlesource.com/c/platform/external/apache-commons-math/+/2702413

Change-Id: I5ad9b2a0822d668b5b6a62933c6d4c1f0b802001
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/src/main/java/org/apache/commons/math3/ode/nonstiff/ThreeEighthesIntegrator.java b/src/main/java/org/apache/commons/math3/ode/nonstiff/ThreeEighthesIntegrator.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.math3.ode.nonstiff;
+
+
+/**
+ * This class implements the 3/8 fourth order Runge-Kutta
+ * integrator for Ordinary Differential Equations.
+ *
+ * <p>This method is an explicit Runge-Kutta method, its Butcher-array
+ * is the following one :
+ * <pre>
+ *    0  |  0    0    0    0
+ *   1/3 | 1/3   0    0    0
+ *   2/3 |-1/3   1    0    0
+ *    1  |  1   -1    1    0
+ *       |--------------------
+ *       | 1/8  3/8  3/8  1/8
+ * </pre>
+ * </p>
+ *
+ * @see EulerIntegrator
+ * @see ClassicalRungeKuttaIntegrator
+ * @see GillIntegrator
+ * @see MidpointIntegrator
+ * @see LutherIntegrator
+ * @since 1.2
+ */
+
+public class ThreeEighthesIntegrator extends RungeKuttaIntegrator {
+
+  /** Time steps Butcher array. */
+  private static final double[] STATIC_C = {
+    1.0 / 3.0, 2.0 / 3.0, 1.0
+  };
+
+  /** Internal weights Butcher array. */
+  private static final double[][] STATIC_A = {
+    {  1.0 / 3.0 },
+    { -1.0 / 3.0, 1.0 },
+    {  1.0, -1.0, 1.0 }
+  };
+
+  /** Propagation weights Butcher array. */
+  private static final double[] STATIC_B = {
+    1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0
+  };
+
+  /** Simple constructor.
+   * Build a 3/8 integrator with the given step.
+   * @param step integration step
+   */
+  public ThreeEighthesIntegrator(final double step) {
+    super("3/8", STATIC_C, STATIC_A, STATIC_B, new ThreeEighthesStepInterpolator(), step);
+  }
+
+}