pub fn vstack<'a, N, I, Iptr, MatArray>(mats: &MatArray) -> CsMatI<N, I, Iptr>where N: 'a + Clone + Default, I: 'a + SpIndex, Iptr: 'a + SpIndex, MatArray: AsRef<[CsMatViewI<'a, N, I, Iptr>]>,
Construct a sparse matrix by vertically stacking other matrices