(commons-statistics) 01/03: Avoid use of Math.pow(x, 2)

[ah...@apache.org]

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aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-statistics.git

commit 25609c1c8d421c642fb5a3b6ae061a372799a917
Author: Alex Herbert <ah...@apache.org>
AuthorDate: Tue Jan 2 09:13:06 2024 +0000

    Avoid use of Math.pow(x, 2)
---
 .../apache/commons/statistics/inference/OneWayAnova.java | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/OneWayAnova.java b/commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/OneWayAnova.java
index 841e331..eb75886 100644
--- a/commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/OneWayAnova.java
+++ b/commons-statistics-inference/src/main/java/org/apache/commons/statistics/inference/OneWayAnova.java
@@ -303,7 +303,7 @@ public final class OneWayAnova {
             }
             // Create the negative sum so we can subtract it via 'add'
             // -sum_g { sum(x)^2/n) }
-            sg.add(-Math.pow(s.getAsDouble(), 2) / array.length);
+            sg.add(-pow2(s.getAsDouble()) / array.length);
         }
 
         // Note: SS terms should not be negative given:
@@ -311,7 +311,7 @@ public final class OneWayAnova {
         // This can happen due to floating-point error in sum(x^2) - sum(x)^2/n
         final double sswg = Math.max(0, sxx.add(sg).getAsDouble());
         // Flip the sign back
-        final double ssbg = Math.max(0, -sg.add(Math.pow(sx.getAsDouble(), 2) / n).getAsDouble());
+        final double ssbg = Math.max(0, -sg.add(pow2(sx.getAsDouble()) / n).getAsDouble());
         final int dfbg = data.size() - 1;
         // Handle edge-cases:
         // Note: 0 / 0 -> NaN : x / 0 -> inf
@@ -332,7 +332,7 @@ public final class OneWayAnova {
         // ni = size of each of the groups
         // nO=(1/(a−1))*(sum(ni)−(sum(ni^2)/sum(ni))
         final double nO = (n - data.stream()
-                .mapToDouble(x -> Math.pow(x.length, 2)).sum() / n) / dfbg;
+                .mapToDouble(x -> pow2(x.length)).sum() / n) / dfbg;
 
         return new Result(dfbg, dfwg, msbg, mswg, nO, f, p);
     }
@@ -372,4 +372,14 @@ public final class OneWayAnova {
         }
         return true;
     }
+
+    /**
+     * Compute {@code x^2}.
+     *
+     * @param x Value.
+     * @return {@code x^2}
+     */
+    private static double pow2(double x) {
+        return x * x;
+    }
 }