Function triu 

pub fn triu<T: Element>(
    a: &Array<T, IxDyn>,
    k: isize,
) -> FerrayResult<Array<T, IxDyn>>

Return the upper triangle of a 2-D array.

k is the diagonal below which to zero elements. 0 = main diagonal.

Analogous to numpy.triu().

Errors

Returns FerrayError::InvalidValue if input is not 2-D.