is_diag.hhs

/**
 * @author Jing Stone
 * @param input - 1d list or 2d matrix
 * @returns - 
 *        Determine if matrix is diagonal, matrix could be rectangular.
 */

function is_diag(input) {
  *import math: ndim
  *import math: deep_copy
  
  // now we're dealing with non-numbers and matrix-like structures:
  // declare raw_in, set it to a input clone if its a Matrix / Tensor otherwise input itself
  let in_type = (input instanceof Mat) || (input instanceof Tensor);
  // here we always maintain raw_in to be an array
  let raw_in = (in_type) ? input.clone().val : deep_copy(input);
  // declare dimension of raw_in
  let dims = ndim(raw_in);

  // true for []
  if (raw_in.length === 0) return true;

  // for 1d list, checkt if the element is 0 exclude raw_in[0]
  if (dims === 1) {
    for (let i = 1; i < raw_in.length; i++) {
      if (raw_in[i] !== 0) {
        return false;
      }
    }
    return true;
  }
  // check other elements except main diagonal are zero or not.
  else if(dims === 2) {
    let row = raw_in.length;
    let col = raw_in[0].length;
    for (let i = 0; i < row; i++) {
      for (let j = 0; j < col; j++) {
        if (i !== j && raw_in[i][j] !== 0)
          return false;
      }
    }
    return true;
  }
  else
  {
    throw new Error("Error in is_diag - input parameter dimension should be 1 or 2");
  }
}