Fix bugs reported by Timothy Hunter:

* CholeskyWithoutSqrt with 1x1 matrices
 * .part<Diagonal>()
Updated unit tests to handle these cases

Eigen/src/Cholesky/CholeskyWithoutSquareRoot.h

@@ -96,6 +96,12 @@ void CholeskyWithoutSquareRoot<MatrixType>::compute(const MatrixType& a)
   m_isPositiveDefinite = true;
   const RealScalar eps = ei_sqrt(precision<Scalar>());
 
+  if (size<=1)
+  {
+    m_matrix = a;
+    return;
+  }
+  
   // Let's preallocate a temporay vector to evaluate the matrix-vector product into it.
   // Unlike the standard Cholesky decomposition, here we cannot evaluate it to the destination
   // matrix because it a sub-row which is not compatible suitable for efficient packet evaluation.

Eigen/src/Core/Part.h

@@ -88,7 +88,7 @@ template<typename MatrixType, unsigned int Mode> class Part
 
     inline Scalar coeff(int row, int col) const
     {
-      if(Flags & LowerTriangularBit ? col>row : row>col)
+      if( (Flags & LowerTriangularBit) && (col>row) || (Flags & UpperTriangularBit) && (row>col) )
         return (Flags & SelfAdjointBit) ? ei_conj(m_matrix.coeff(col, row)) : (Scalar)0;
       if(Flags & UnitDiagBit)
         return col==row ? (Scalar)1 : m_matrix.coeff(row, col);

test/cholesky.cpp

@@ -79,7 +79,6 @@ template<typename MatrixType> void cholesky(const MatrixType& m)
   }
   #endif
 
-  if (rows>1)
   {
     CholeskyWithoutSquareRoot<SquareMatrixType> cholnosqrt(symm);
     VERIFY(cholnosqrt.isPositiveDefinite());

test/triangular.cpp

@@ -81,6 +81,8 @@ template<typename MatrixType> void triangular(const MatrixType& m)
   m1.template part<Eigen::Lower>() = (m2.transpose() * m2).lazy();
   VERIFY_IS_APPROX(m3.template part<Eigen::Lower>(), m1);
 
+  VERIFY_IS_APPROX(m3.template part<Diagonal>(), m3.diagonal().asDiagonal());
+
   m1 = MatrixType::Random(rows, cols);
   for (int i=0; i<rows; ++i)
     while (ei_abs2(m1(i,i))<1e-3) m1(i,i) = ei_random<Scalar>();