From 9234883914cc84dd412a3f600d3bfc09e364388c Mon Sep 17 00:00:00 2001
From: Tyler Veness <calcmogul@gmail.com>
Date: Mon, 27 Oct 2025 22:06:59 +0000
Subject: [PATCH] Fix SparseVector::insert(Index) assigning int to Scalar
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Scalar doesn't necessarily support implicit construction from int or
assignment from int.

Here's the error message I got without this fix:
```
/home/tav/git/Sleipnir/build/_deps/eigen3-src/Eigen/src/SparseCore/SparseVector.h:180:25: error: no match for ‘operator=’ (operand types are ‘Eigen::internal::CompressedStorage<ExplicitDouble, int>::Scalar’ {aka ‘ExplicitDouble’} and ‘int’)
  180 |     m_data.value(p + 1) = 0;
      |     ~~~~~~~~~~~~~~~~~~~~^~~
```

See merge request libeigen/eigen!2046
---
 Eigen/src/SparseCore/SparseVector.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Eigen/src/SparseCore/SparseVector.h b/Eigen/src/SparseCore/SparseVector.h
index 8b34a9ac9..c8d34e318 100644
--- a/Eigen/src/SparseCore/SparseVector.h
+++ b/Eigen/src/SparseCore/SparseVector.h
@@ -177,7 +177,7 @@ class SparseVector : public SparseCompressedBase<SparseVector<Scalar_, Options_,
       --p;
     }
     m_data.index(p + 1) = convert_index(i);
-    m_data.value(p + 1) = 0;
+    m_data.value(p + 1) = Scalar(0);
     return m_data.value(p + 1);
   }