code: function identSize(M, m, n, k) {
                  var e = M.elements;
                  var i = k - 1;
  
                  while(i--) {
              	var row = [];
              	
              	for(var j = 0; j < n; j++)
              	    row.push(j == i ? 1 : 0);
              	
                      e.unshift(row);
                  }
                  
                  for(var i = k - 1; i < m; i++) {
                      while(e[i].length < n)
                          e[i].unshift(0);
                  }
  
                  return $M(e);
              }
docs: Copyright (c) 2011, Chris Umbel, James Coglan Matrix class - depends on Vector. augment a matrix M with identity rows/cols