From f80d7b8254ff9185417f2aaa6e1796a48cf944a8 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <4643818-rmlarsen1@users.noreply.gitlab.com>
Date: Sun, 8 Mar 2026 16:00:04 -0700
Subject: [PATCH] Fix three more flaky tests: igamma, tensor_random,
 matrix_power

libeigen/eigen!2268

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>
---
 .../SpecialFunctions/SpecialFunctionsImpl.h   |  8 +++++-
 unsupported/test/cxx11_tensor_random.cpp      | 27 ++++++++++++++++---
 unsupported/test/matrix_power.cpp             |  8 +++---
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h b/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h
index 8e88b9dd9..83eada37f 100644
--- a/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h
+++ b/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h
@@ -1165,7 +1165,13 @@ struct igamma_generic_impl {
       }
     }
 
-    return igamma_series_impl<Scalar, mode>::run(a, x);
+    Scalar ret = igamma_series_impl<Scalar, mode>::run(a, x);
+    if (mode == VALUE) {
+      // Clamp to [0,1] since accumulated series terms can slightly exceed 1.0
+      // due to floating-point rounding for extreme arguments.
+      return numext::mini(one, numext::maxi(zero, ret));
+    }
+    return ret;
   }
 };
 
diff --git a/unsupported/test/cxx11_tensor_random.cpp b/unsupported/test/cxx11_tensor_random.cpp
index b1dc6e4c1..db370a6a8 100644
--- a/unsupported/test/cxx11_tensor_random.cpp
+++ b/unsupported/test/cxx11_tensor_random.cpp
@@ -18,8 +18,19 @@ static void test_default() {
 
   // Fixme: we should check that the generated numbers follow a uniform
   // distribution instead.
-  for (int i = 1; i < 6; ++i) {
-    VERIFY_IS_NOT_EQUAL(vec(i), vec(i - 1));
+  // For low-precision types (half, bfloat16), the RNG has limited distinct
+  // values (e.g. 128 for bfloat16), so adjacent collisions are statistically
+  // inevitable. Only verify that not all values are identical.
+  if (sizeof(Scalar) <= 2) {
+    bool has_distinct = false;
+    for (int i = 1; i < 6 && !has_distinct; ++i) {
+      if (vec(i) != vec(i - 1)) has_distinct = true;
+    }
+    VERIFY(has_distinct);
+  } else {
+    for (int i = 1; i < 6; ++i) {
+      VERIFY_IS_NOT_EQUAL(vec(i), vec(i - 1));
+    }
   }
 }
 
@@ -30,8 +41,16 @@ static void test_normal() {
 
   // Fixme: we should check that the generated numbers follow a gaussian
   // distribution instead.
-  for (int i = 1; i < 6; ++i) {
-    VERIFY_IS_NOT_EQUAL(vec(i), vec(i - 1));
+  if (sizeof(Scalar) <= 2) {
+    bool has_distinct = false;
+    for (int i = 1; i < 6 && !has_distinct; ++i) {
+      if (vec(i) != vec(i - 1)) has_distinct = true;
+    }
+    VERIFY(has_distinct);
+  } else {
+    for (int i = 1; i < 6; ++i) {
+      VERIFY_IS_NOT_EQUAL(vec(i), vec(i - 1));
+    }
   }
 }
 
diff --git a/unsupported/test/matrix_power.cpp b/unsupported/test/matrix_power.cpp
index e17d35ae6..7b449bc9e 100644
--- a/unsupported/test/matrix_power.cpp
+++ b/unsupported/test/matrix_power.cpp
@@ -152,7 +152,7 @@ EIGEN_DECLARE_TEST(matrix_power) {
   CALL_SUBTEST_1(test2dHyperbolicRotation<float>(1e-5f));
   CALL_SUBTEST_9(test2dHyperbolicRotation<long double>(1e-14L));
 
-  CALL_SUBTEST_10(test3dRotation<double>(1e-13));
+  CALL_SUBTEST_10(test3dRotation<double>(2e-13));
   CALL_SUBTEST_11(test3dRotation<float>(1e-5f));
   CALL_SUBTEST_12(test3dRotation<long double>(1e-13L));
 
@@ -165,7 +165,7 @@ EIGEN_DECLARE_TEST(matrix_power) {
   CALL_SUBTEST_8(testGeneral(Matrix4f(), 1e-4f));
   CALL_SUBTEST_6(testGeneral(MatrixXf(2, 2), 1e-3f));  // see bug 614
   CALL_SUBTEST_9(testGeneral(MatrixXe(7, 7), 1e-12L));
-  CALL_SUBTEST_10(testGeneral(Matrix3d(), 1e-13));
+  CALL_SUBTEST_10(testGeneral(Matrix3d(), 2e-13));
   CALL_SUBTEST_11(testGeneral(Matrix3f(), 1e-4f));
   CALL_SUBTEST_12(testGeneral(Matrix3e(), 1e-13L));
 
@@ -178,7 +178,7 @@ EIGEN_DECLARE_TEST(matrix_power) {
   CALL_SUBTEST_8(testSingular(Matrix4f(), 1e-4f));
   CALL_SUBTEST_6(testSingular(MatrixXf(2, 2), 1e-3f));
   CALL_SUBTEST_9(testSingular(MatrixXe(7, 7), 1e-12L));
-  CALL_SUBTEST_10(testSingular(Matrix3d(), 1e-13));
+  CALL_SUBTEST_10(testSingular(Matrix3d(), 2e-13));
   CALL_SUBTEST_11(testSingular(Matrix3f(), 1e-4f));
   CALL_SUBTEST_12(testSingular(Matrix3e(), 1e-13L));
 
@@ -191,7 +191,7 @@ EIGEN_DECLARE_TEST(matrix_power) {
   CALL_SUBTEST_8(testLogThenExp(Matrix4f(), 1e-4f));
   CALL_SUBTEST_6(testLogThenExp(MatrixXf(2, 2), 1e-3f));
   CALL_SUBTEST_9(testLogThenExp(MatrixXe(7, 7), 1e-12L));
-  CALL_SUBTEST_10(testLogThenExp(Matrix3d(), 1e-13));
+  CALL_SUBTEST_10(testLogThenExp(Matrix3d(), 2e-13));
   CALL_SUBTEST_11(testLogThenExp(Matrix3f(), 1e-4f));
   CALL_SUBTEST_12(testLogThenExp(Matrix3e(), 1e-13L));
 }