From f928159ed6c25c4aec01adebf2c4d1211c3dc006 Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Fri, 6 Dec 2024 18:10:01 +0100
Subject: [PATCH] PERF: Use `vnl_sparse_matrix::get` in ComputeJacobianTerms

`vnl_sparse_matrix::get(r, c)` just returns when the entry isn't there, and it returns immediately when the row is empty.

A performance improvement may not be noticeable, but it won't harm.
---
 Common/itkComputeJacobianTerms.hxx | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/Common/itkComputeJacobianTerms.hxx b/Common/itkComputeJacobianTerms.hxx
index ca890a883..abd9c203c 100644
--- a/Common/itkComputeJacobianTerms.hxx
+++ b/Common/itkComputeJacobianTerms.hxx
@@ -312,13 +312,10 @@ ComputeJacobianTerms<TFixedImage, TTransform>::Compute() const -> Terms
   double TrC = 0.0;
   for (unsigned int p = 0; p < numberOfParameters; ++p)
   {
-    if (!cov.empty_row(p))
-    {
-      // avoid creation of element if the row is empty
-      CovarianceValueType & covpp = cov(p, p);
-      TrC += covpp;
-      diagcov[p] = covpp;
-    }
+    // Do cov.get(p, p) instead of cov(p, p) to avoid creation of an entry that just has zero.
+    const CovarianceValueType covpp = cov.get(p, p);
+    TrC += covpp;
+    diagcov[p] = covpp;
   }
 
   /**