Function unflatten_pair 

pub fn unflatten_pair<B: Backend, const DA: usize, const DB: usize>(
    combined: <B as BackendTypes>::FloatTensorPrimitive,
    flat_y_len: usize,
    flat_s_len: usize,
    shape_y: [usize; DA],
    shape_s: [usize; DB],
) -> (<B as BackendTypes>::FloatTensorPrimitive, <B as BackendTypes>::FloatTensorPrimitive)

Inverse of flatten_pair: split a 1-D combined tensor back into the two outputs at their original ranks/shapes.