From 0792ef87893af0946611d45a57e73a63f12dcb9a Mon Sep 17 00:00:00 2001
From: yuki takehara <y.takehara1014@gmail.com>
Date: Tue, 13 Mar 2018 03:49:10 +0900
Subject: [PATCH] Merge pull request #11049 from take1014:#10948

* Fix #10948

* Add test code

* Fixed build error

* Add value zero

* eigen: test cleanup
---
 modules/core/src/lda.cpp         |  5 ++++-
 modules/core/test/test_eigen.cpp | 11 +++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/modules/core/src/lda.cpp b/modules/core/src/lda.cpp
index 48b7391805..5acdb24c62 100644
--- a/modules/core/src/lda.cpp
+++ b/modules/core/src/lda.cpp
@@ -350,6 +350,9 @@ private:
             // Look for single small sub-diagonal element
             int l = n1;
             while (l > low) {
+                if (norm < FLT_EPSILON) {
+                    break;
+                }
                 s = std::abs(H[l - 1][l - 1]) + std::abs(H[l][l]);
                 if (s == 0.0) {
                     s = norm;
@@ -594,7 +597,7 @@ private:
 
         // Backsubstitute to find vectors of upper triangular form
 
-        if (norm == 0.0) {
+        if (norm < FLT_EPSILON) {
             return;
         }
 
diff --git a/modules/core/test/test_eigen.cpp b/modules/core/test/test_eigen.cpp
index c059311ff3..8a90c6e325 100644
--- a/modules/core/test/test_eigen.cpp
+++ b/modules/core/test/test_eigen.cpp
@@ -516,4 +516,15 @@ static void testEigen3x3()
 TEST(Core_EigenNonSymmetric, float3x3) { testEigen3x3<float>(); }
 TEST(Core_EigenNonSymmetric, double3x3) { testEigen3x3<double>(); }
 
+typedef testing::TestWithParam<int> Core_EigenZero;
+TEST_P(Core_EigenZero, double)
+{
+    int N = GetParam();
+    Mat_<double> srcZero = Mat_<double>::zeros(N, N);
+    Mat_<double> expected_eigenvalueZero = Mat_<double>::zeros(N, 1);  // 1D Mat
+    testEigen(srcZero, expected_eigenvalueZero);
+    testEigen(srcZero, expected_eigenvalueZero, true);
+}
+INSTANTIATE_TEST_CASE_P(/**/, Core_EigenZero, testing::Values(2, 3, 5));
+
 }} // namespace
-- 
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