How do you insert vertical or horizontal line in graph of the function in matlab for testing whether it is function or not?

In MATLAB, you can insert vertical or horizontal lines on a graph by using the xline or yline functions, respectively. For example, to add a vertical line at ( x = a ), use xline(a, 'r--'), and for a horizontal line at ( y = b ), use yline(b, 'g--'). These lines can help you visually test if a given relation defines a function by checking if any vertical line intersects the graph at more than one point (the vertical line test).