From 70c0174bf9cb0a7dd22c47e377f9b9efc22ba4c9 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Mon, 23 Mar 2009 14:44:44 +0000
Subject: [PATCH] * allows fixed size matrix with size==0 (via a specialization
 of   MatrixStorage returning a null pointer). For instance this is very  
 useful to make Tridiagonalization compile for 1x1 matrices * fix LLT and
 eigensolver for 1x1 matrix

---
 Eigen/src/Cholesky/LLT.h              |  2 ++
 Eigen/src/Core/Block.h                |  4 ++--
 Eigen/src/Core/Matrix.h               |  8 +++-----
 Eigen/src/Core/MatrixStorage.h        | 15 +++++++++++++++
 Eigen/src/QR/SelfAdjointEigenSolver.h |  8 ++++++++
 5 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/Eigen/src/Cholesky/LLT.h b/Eigen/src/Cholesky/LLT.h
index e02b82551..66b86a204 100644
--- a/Eigen/src/Cholesky/LLT.h
+++ b/Eigen/src/Cholesky/LLT.h
@@ -103,6 +103,8 @@ void LLT<MatrixType>::compute(const MatrixType& a)
   x = ei_real(a.coeff(0,0));
   m_isPositiveDefinite = x > eps && ei_isMuchSmallerThan(ei_imag(a.coeff(0,0)), RealScalar(1));
   m_matrix.coeffRef(0,0) = ei_sqrt(x);
+  if(size==1)
+    return;
   m_matrix.col(0).end(size-1) = a.row(0).end(size-1).adjoint() / ei_real(m_matrix.coeff(0,0));
   for (int j = 1; j < size; ++j)
   {
diff --git a/Eigen/src/Core/Block.h b/Eigen/src/Core/Block.h
index 195533266..2473864d3 100644
--- a/Eigen/src/Core/Block.h
+++ b/Eigen/src/Core/Block.h
@@ -68,8 +68,8 @@ struct ei_traits<Block<MatrixType, BlockRows, BlockCols, _PacketAccess, _DirectA
   typedef typename MatrixType::Nested MatrixTypeNested;
   typedef typename ei_unref<MatrixTypeNested>::type _MatrixTypeNested;
   enum{
-    RowsAtCompileTime = MatrixType::RowsAtCompileTime == 1 ? 1 : BlockRows,
-    ColsAtCompileTime = MatrixType::ColsAtCompileTime == 1 ? 1 : BlockCols,
+    RowsAtCompileTime = BlockRows,
+    ColsAtCompileTime = BlockCols,
     MaxRowsAtCompileTime = RowsAtCompileTime == 1 ? 1
       : (BlockRows==Dynamic ? MatrixType::MaxRowsAtCompileTime : BlockRows),
     MaxColsAtCompileTime = ColsAtCompileTime == 1 ? 1
diff --git a/Eigen/src/Core/Matrix.h b/Eigen/src/Core/Matrix.h
index fbd55e526..99f89356d 100644
--- a/Eigen/src/Core/Matrix.h
+++ b/Eigen/src/Core/Matrix.h
@@ -534,11 +534,9 @@ class Matrix
 
     static EIGEN_STRONG_INLINE void _check_template_params()
     {
-        EIGEN_STATIC_ASSERT((_Rows > 0
-                        && _Cols > 0
-                        && _MaxRows <= _Rows
-                        && _MaxCols <= _Cols
-                        && (_Options & (AutoAlign|RowMajor)) == _Options),
+        EIGEN_STATIC_ASSERT(((_MaxRows >= _Rows || _Rows==Dynamic)
+                          && (_MaxCols >= _Cols || _Cols==Dynamic)
+                          && (_Options & (AutoAlign|RowMajor)) == _Options),
           INVALID_MATRIX_TEMPLATE_PARAMETERS)
     }
 };
diff --git a/Eigen/src/Core/MatrixStorage.h b/Eigen/src/Core/MatrixStorage.h
index ba2355b8e..e3ddec433 100644
--- a/Eigen/src/Core/MatrixStorage.h
+++ b/Eigen/src/Core/MatrixStorage.h
@@ -85,6 +85,21 @@ template<typename T, int Size, int _Rows, int _Cols, int _Options> class ei_matr
     inline T *data() { return m_data.array; }
 };
 
+// null matrix
+template<typename T, int _Rows, int _Cols, int _Options> class ei_matrix_storage<T, 0, _Rows, _Cols, _Options>
+{
+  public:
+    inline explicit ei_matrix_storage() {}
+    inline ei_matrix_storage(ei_constructor_without_unaligned_array_assert) {}
+    inline ei_matrix_storage(int,int,int) {}
+    inline void swap(ei_matrix_storage& other) {}
+    inline static int rows(void) {return _Rows;}
+    inline static int cols(void) {return _Cols;}
+    inline void resize(int,int,int) {}
+    inline const T *data() const { return 0; }
+    inline T *data() { return 0; }
+};
+
 // dynamic-size matrix with fixed-size storage
 template<typename T, int Size, int _Options> class ei_matrix_storage<T, Size, Dynamic, Dynamic, _Options>
 {
diff --git a/Eigen/src/QR/SelfAdjointEigenSolver.h b/Eigen/src/QR/SelfAdjointEigenSolver.h
index 1c9ad513d..6d3bdf005 100644
--- a/Eigen/src/QR/SelfAdjointEigenSolver.h
+++ b/Eigen/src/QR/SelfAdjointEigenSolver.h
@@ -189,6 +189,14 @@ void SelfAdjointEigenSolver<MatrixType>::compute(const MatrixType& matrix, bool
   assert(matrix.cols() == matrix.rows());
   int n = matrix.cols();
   m_eivalues.resize(n,1);
+
+  if(n==1)
+  {
+    m_eivalues.coeffRef(0,0) = ei_real(matrix.coeff(0,0));
+    m_eivec.setOnes();
+    return;
+  }
+
   m_eivec = matrix;
 
   // FIXME, should tridiag be a local variable of this function or an attribute of SelfAdjointEigenSolver ?