The definition for doubly stochastic matrix can be found here. We say a square matrix $A$ is a Generalized doubly stochastic matrix if the sum of each rows and columns of $A$ all equals 1. But A doesn't have to be non-negative.
An interesting fact(which is also easy to prove) about doubly stochastic matrix is: if $A$ is doubly stochastic and orthogonal, then $A$ is actually a permutation matrix.
So my question is: what is the intersection set for a generalized doubly stochastic matrix set and orthogonal matrix set?
More specifically, can any one give me an example of an $N \times N$ matrix $A$, which satisfy the following constraints:
- $AA^T=I$
- $A*1=1$
- $A^T*1=1$
- there exists at least one entry $A_{i,j}$, satisfying $A_{i,j}<0$
Thanks!