Function tensor_contraction 

pub fn tensor_contraction(
    a: &DenseTensor,
    mode_a: usize,
    b: &DenseTensor,
    mode_b: usize,
) -> DenseTensor

Tensor contraction: contract modes mode_a of a and mode_b of b over their shared dimension.

For rank-2 tensors this reduces to matrix–matrix multiplication when mode_a == 1 (col) and mode_b == 0 (row).