Function tril 

pub fn tril<T>(
    array: &dyn SparseArray<T>,
    k: isize,
    format: &str,
) -> SparseResult<Box<dyn SparseArray<T>>>
where
    T: Float + Add<Output = T> + Sub<Output = T> + Mul<Output = T> + Div<Output = T> + Debug + Copy + 'static,

Extract lower triangular part of a sparse array

Arguments

• array - The input sparse array
• k - Diagonal offset (0 = main diagonal, >0 = above main, <0 = below main)
• format - Format of the output array (“csr” or “coo”)

Returns

A sparse array containing the lower triangular part

Examples

use scirs2_sparse::construct::eye_array;
use scirs2_sparse::combine::tril;

let a: Box<dyn scirs2_sparse::SparseArray<f64>> = eye_array(3, "csr").unwrap();
let b = tril(&*a, 0, "csr").unwrap();

assert_eq!(b.shape(), (3, 3));
assert_eq!(b.get(0, 0), 1.0);
assert_eq!(b.get(1, 1), 1.0);
assert_eq!(b.get(2, 2), 1.0);
assert_eq!(b.get(1, 0), 0.0);  // No non-zero elements below diagonal

// With k=1, include first superdiagonal
let c = tril(&*a, 1, "csr").unwrap();
assert_eq!(c.get(0, 1), 0.0);  // Nothing in superdiagonal of identity matrix