*add operator()(int) for vectors, synonymous to operator[](int).

I don't see any reason not to allow it, it doesn't add much code, and
 it makes porting from eigen1 easier.
*expand tests/basicstuff to first test coefficient access methods

Eigen/src/Core/Coeffs.h

@@ -134,6 +134,23 @@ inline const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
   return derived().coeff(index);
 }
 
+/** \returns the coefficient at given index.
+  *
+  * This is synonymous to operator[](int) const.
+  *
+  * This method is allowed only for vector expressions, and for matrix expressions having the LinearAccessBit.
+  *
+  * \sa operator[](int), operator()(int,int) const, x() const, y() const,
+  * z() const, w() const
+  */
+template<typename Derived>
+inline const typename ei_traits<Derived>::Scalar MatrixBase<Derived>
+  ::operator()(int index) const
+{
+  ei_assert(index >= 0 && index < size());
+  return derived().coeff(index);
+}
+
 /** Short version: don't use this function, use
   * \link operator[](int) \endlink instead.
   *
@@ -170,6 +187,22 @@ inline typename ei_traits<Derived>::Scalar& MatrixBase<Derived>
   return derived().coeffRef(index);
 }
 
+/** \returns a reference to the coefficient at given index.
+  *
+  * This is synonymous to operator[](int).
+  *
+  * This method is allowed only for vector expressions, and for matrix expressions having the LinearAccessBit.
+  *
+  * \sa operator[](int) const, operator()(int,int), x(), y(), z(), w()
+  */
+template<typename Derived>
+inline typename ei_traits<Derived>::Scalar& MatrixBase<Derived>
+  ::operator()(int index)
+{
+  ei_assert(index >= 0 && index < size());
+  return derived().coeffRef(index);
+}
+
 /** equivalent to operator[](0).  */
 template<typename Derived>
 inline const typename ei_traits<Derived>::Scalar MatrixBase<Derived>

Eigen/src/Core/MatrixBase.h

@@ -249,9 +249,11 @@ template<typename Derived> class MatrixBase
 
     const Scalar coeff(int index) const;
     const Scalar operator[](int index) const;
+    const Scalar operator()(int index) const;
 
     Scalar& coeffRef(int index);
     Scalar& operator[](int index);
+    Scalar& operator()(int index);
 
     template<typename OtherDerived>
     void copyCoeff(int row, int col, const MatrixBase<OtherDerived>& other);

test/basicstuff.cpp

@@ -46,9 +46,22 @@ template<typename MatrixType> void basicStuff(const MatrixType& m)
              v2 = VectorType::Random(rows),
              vzero = VectorType::Zero(rows);
 
+  Scalar x = ei_random<Scalar>();
+
   int r = ei_random<int>(0, rows-1),
       c = ei_random<int>(0, cols-1);
 
+  m1.coeffRef(r,c) = x;
+  VERIFY_IS_APPROX(x, m1.coeff(r,c));
+  m1(r,c) = x;
+  VERIFY_IS_APPROX(x, m1(r,c));
+  v1.coeffRef(r) = x;
+  VERIFY_IS_APPROX(x, v1.coeff(r));
+  v1(r) = x;
+  VERIFY_IS_APPROX(x, v1(r));
+  v1[r] = x;
+  VERIFY_IS_APPROX(x, v1[r]);
+
   VERIFY_IS_APPROX(               v1,    v1);
   VERIFY_IS_NOT_APPROX(           v1,    2*v1);
   VERIFY_IS_MUCH_SMALLER_THAN(    vzero, v1);