Return whether extremum is minimum or maximum

shred · Nov 27, 2017 · f3e471a · f3e471a
1 parent 57f4286
commit f3e471a
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Showing 2 changed files with 27 additions and 1 deletion.
diff --git a/src/main/java/org/shredzone/commons/suncalc/util/QuadraticInterpolation.java b/src/main/java/org/shredzone/commons/suncalc/util/QuadraticInterpolation.java
@@ -25,6 +25,7 @@ public class QuadraticInterpolation {
     private final double root1;
     private final double root2;
     private final int nRoot;
+    private final boolean maximum;
 
     /**
      * Creates a new quadratic equation.
@@ -43,6 +44,7 @@ public QuadraticInterpolation(double yMinus, double y0, double yPlus) {
 
         xe = -b / (2.0 * a);
         ye = (a * xe + b) * xe + c;
+        maximum = a < 0.0;
         double dis = b * b - 4.0 * a * c;
 
         int rootCount = 0;
@@ -112,4 +114,14 @@ public int getNumberOfRoots() {
         return nRoot;
     }
 
+    /**
+     * Returns whether the extremum is a minimum or a maximum.
+     *
+     * @return {@code true}: Extremum at xe is a maximum. {@code false}: Extremum at xe is
+     *         a minimum.
+     */
+    public boolean isMaximum() {
+        return maximum;
+    }
+
 }
diff --git a/src/test/java/org/shredzone/commons/suncalc/util/QuadraticInterpolationTest.java b/src/test/java/org/shredzone/commons/suncalc/util/QuadraticInterpolationTest.java
@@ -26,14 +26,27 @@ public class QuadraticInterpolationTest {
     private static final double ERROR = 0.001;
 
     @Test
-    public void testTwoRoots() {
+    public void testTwoRootsAndMinimum() {
         QuadraticInterpolation qi = new QuadraticInterpolation(1.0, -1.0, 1.0);
 
         assertThat(qi.getNumberOfRoots(), is(2));
         assertThat(qi.getRoot1(), is(closeTo(-0.707, ERROR)));
         assertThat(qi.getRoot2(), is(closeTo( 0.707, ERROR)));
         assertThat(qi.getXe(), is(closeTo( 0.0, ERROR)));
         assertThat(qi.getYe(), is(closeTo(-1.0, ERROR)));
+        assertThat(qi.isMaximum(), is(false));
+    }
+
+    @Test
+    public void testTwoRootsAndMaximum() {
+        QuadraticInterpolation qi = new QuadraticInterpolation(-1.0, 1.0, -1.0);
+
+        assertThat(qi.getNumberOfRoots(), is(2));
+        assertThat(qi.getRoot1(), is(closeTo(-0.707, ERROR)));
+        assertThat(qi.getRoot2(), is(closeTo( 0.707, ERROR)));
+        assertThat(qi.getXe(), is(closeTo(0.0, ERROR)));
+        assertThat(qi.getYe(), is(closeTo(1.0, ERROR)));
+        assertThat(qi.isMaximum(), is(true));
     }
 
     @Test
@@ -44,6 +57,7 @@ public void testOneRoot() {
         assertThat(qi.getRoot1(), is(closeTo( 0.0, ERROR)));
         assertThat(qi.getXe(), is(closeTo( 1.5, ERROR)));
         assertThat(qi.getYe(), is(closeTo(-1.125, ERROR)));
+        assertThat(qi.isMaximum(), is(false));
     }
 
     @Test