Merge pull request #371 from Serrof/issue-370

Serrof · web-flow · commit 3a25a68649fc · 2025-02-06T22:26:45.000+01:00
add native way to stack an independent variable in (Field)Gradient
diff --git a/hipparchus-core/src/changes/changes.xml b/hipparchus-core/src/changes/changes.xml
@@ -50,7 +50,10 @@ If the output is not quite correct, check for invisible trailing spaces!
   </properties>
   <body>
     <release version="4.0" date="TBD" description="TBD">
-      <action dev="luc" type="fix" issue="issuers/360">
+      <action dev="serrof" type="add" issue="issues/370">
+        Added native way to stack an independent variable in (Field)Gradient.
+      </action>
+      <action dev="luc" type="fix" issue="issues/360">
         Increased dimension of directions numbers in Sobol sequence generation.
       </action>
       <action dev="luc" type="fix" issue="issues/354">
diff --git a/hipparchus-core/src/main/java/org/hipparchus/analysis/differentiation/FieldGradient.java b/hipparchus-core/src/main/java/org/hipparchus/analysis/differentiation/FieldGradient.java
@@ -877,6 +877,17 @@ public FieldGradient<T> linearCombination(final double a1, final FieldGradient<T
         return result;
     }
 
+    /**
+     * Add an independent variable to the Taylor expansion.
+     * @return object with one more variable
+     * @since 13.0
+     */
+    public FieldGradient<T> stackVariable() {
+        final T[] gradient = MathArrays.buildArray(getValueField(), this.getFreeParameters() + 1);
+        System.arraycopy(this.grad, 0, gradient, 0, this.getFreeParameters());
+        return new FieldGradient<>(this.value, gradient);
+    }
+
     /** {@inheritDoc} */
     @Override
     public FieldGradient<T> getPi() {
diff --git a/hipparchus-core/src/main/java/org/hipparchus/analysis/differentiation/Gradient.java b/hipparchus-core/src/main/java/org/hipparchus/analysis/differentiation/Gradient.java
@@ -712,6 +712,17 @@ public Gradient linearCombination(final double a1, final Gradient b1,
         return result;
     }
 
+    /**
+     * Add an independent variable to the Taylor expansion.
+     * @return object with one more variable
+     * @since 13.0
+     */
+    public Gradient stackVariable() {
+        final double[] gradient = new double[this.getFreeParameters() + 1];
+        System.arraycopy(this.grad, 0, gradient, 0, this.getFreeParameters());
+        return new Gradient(gradient, this.getValue());
+    }
+
     /** Test for the equality of two univariate derivatives.
      * <p>
      * univariate derivatives are considered equal if they have the same derivatives.
diff --git a/hipparchus-core/src/test/java/org/hipparchus/analysis/differentiation/FieldGradientTest.java b/hipparchus-core/src/test/java/org/hipparchus/analysis/differentiation/FieldGradientTest.java
@@ -0,0 +1,39 @@
+/*
+ * Licensed to the Hipparchus project under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The Hipparchus project 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
+ *
+ *      https://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.hipparchus.analysis.differentiation;
+
+import org.hipparchus.complex.Complex;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+class FieldGradientTest {
+
+    @Test
+    void testStackVariable() {
+        // GIVEN
+        final FieldGradient<Complex> gradient = new FieldGradient<>(Complex.ONE, new Complex(2));
+        // WHEN
+        final FieldGradient<Complex> gradientWithMoreVariable = gradient.stackVariable();
+        // THEN
+        Assertions.assertEquals(gradient.getValue(), gradientWithMoreVariable.getValue());
+        Assertions.assertEquals(gradient.getFreeParameters() + 1, gradientWithMoreVariable.getFreeParameters());
+        Assertions.assertArrayEquals(gradient.getGradient(), Arrays.copyOfRange(gradientWithMoreVariable.getGradient(),
+                0, gradient.getFreeParameters()));
+    }
+}
diff --git a/hipparchus-core/src/test/java/org/hipparchus/analysis/differentiation/GradientTest.java b/hipparchus-core/src/test/java/org/hipparchus/analysis/differentiation/GradientTest.java
@@ -26,8 +26,11 @@
 import org.hipparchus.util.FastMath;
 import org.hipparchus.util.FieldSinCos;
 import org.hipparchus.util.MathArrays;
+import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import java.util.Arrays;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertNotSame;
@@ -91,6 +94,19 @@ void testVariable() {
         }
     }
 
+    @Test
+    void testStackVariable() {
+        // GIVEN
+        final Gradient gradient = new Gradient(1, 2, 3);
+        // WHEN
+        final Gradient gradientWithMoreVariable = gradient.stackVariable();
+        // THEN
+        Assertions.assertEquals(gradient.getValue(), gradientWithMoreVariable.getValue());
+        Assertions.assertEquals(gradient.getFreeParameters() + 1, gradientWithMoreVariable.getFreeParameters());
+        Assertions.assertArrayEquals(gradient.getGradient(), Arrays.copyOfRange(gradientWithMoreVariable.getGradient(),
+                0, gradient.getFreeParameters()));
+    }
+
     @Test
     void testDoublePow() {
         assertSame(build(3).getField().getZero(), Gradient.pow(0.0, build(1.5)));
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
@@ -50,6 +50,9 @@ If the output is not quite correct, check for invisible trailing spaces!
   </properties>
   <body>
     <release version="4.0" date="TBD" description="TBD">
+      <action dev="serrof" type="add" issue="issues/370">
+        Added native way to stack an independent variable in (Field)Gradient.
+      </action>
       <action dev="luc" type="fix" issue="issues/368">
         Added point, hyperplane and sub-hyperplane types to geometry classes parameters
       </action>
