The files plot the graphs of continuous functions; vertical segments may appear at points of discontinuity.
Only a grid of horizontal lines is drawn automatically and the interval of the abscissas is chosen so as to contain all the points.
In these cases (y = |x|; y = −3+1.3·|x−2|−0.1·|x-2|^2 with x from −8 to 17) axes have been plotted.  How did we proceed?

In the first case  ( y=|x| )  (0,0) is (input, output) of the function in the center of [-2,2].
The point corresponds to (x[500], y[500]). We trace, starting at (0,0) and returning to (0,0), the two segments: (0,-2.95)-(0,2.95) and (-2,0)-(2-0).

``` array("x" => \$x[500], "y" => \$y[500]),

array("x" => 0, "y" => 2.95),
array("x" => 0, "y" => -2.95),
array("x" => 0, "y" => 0),
array("x" => -2, "y" => 0),
array("x" => 2, "y" => 0),
array("x" => 0, "y" => 0),
array("x" => \$x[500], "y" => \$y[500]),
...
array("x" => \$x[1000], "y" => \$y[1000])
);```

In the second case  (  F  )  if I want to consider an interval - [−17,17] - that is wider than the domain - [−8,17] - I have to find the value between x[0] (ie -8),..., x[1000] (ie 17) which corresponds to 0.
In this case  (0 − − 8) / (17 − − 8) · 1000  is 320.

```\$a= -8; \$b= 17;
\$n=1000; \$x = array(); \$y = array();
...
array("x" => \$x[320], "y" => \$y[320]),

array("x" => 0, "y" => 0),
array("x" => 0, "y" => 7.85),
array("x" => 0, "y" => -7.85),
array("x" => 0, "y" => 0),
array("x" => -17, "y" => 0),
array("x" => 17, "y" => 0),
array("x" => 0, "y" => 0),
...
array("x" => \$x[1000], "y" => \$y[1000])
);
```