Void matrices

    A matrix (vector, row vector, or column vector) that is 0 x 0, r x 0, or 0 x c is said to be void; see [M-2]
    void.

    The function J(r, c, val) returns an r x c matrix with each element containing val; see [M-5] J().

    J() can be used to create void matrices.

    See [M-2] void.

谢谢解答。我也看到这个，但怎么 mat A=J(0,0,.)总报错，是不是需要在mata下使用？

这个是mata的

非常感谢