[eigen] Using transpose in expressions

[Brad Bell <bradbell@xxxxxxxxxx>]

Why does the following program  work when ERROR_CASE is zero and 
generates a compile error when ERROR_CASE is one
(I am using eigen-3.2.7).

# include <iostream>
# include <Eigen/Core>
# define ERROR_CASE 1
int main(void)
{   typedef Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic> matrix;
    //
    matrix A = matrix::Identity(2, 2);
# if ERROR_CASE
    matrix C = A * (A * A).transpose();
# else
    matrix C = A * A * A.transpose();
# endif
    //
    std::cout << "C = \n" << C << "\n";
}