One of the questions I am sometimes asked is, “If I need a specific x-value to appear in my graphical function, how do I determine the number of points required to include that exact point?” This arises because in a graphical function, the x-axis is divided into fixed intervals; the user is only allowed to specify x-min, x-max, and the number of data points. [If you really need a graphical function with arbitrary (x, y) points, use the LOOKUPXY() built-in function available in version 9.1.2.]
For the following discussion, the range on the x-axis will be needed:
range = x_max – x_min
In all of the examples below, x_min = 3.000 and x_max = 7.000, so the range = 7 – 3 = 4.
For integer values, here is a simple formula that always works:
# of data points = range + 1 (1)
For example (using the range above), if the number 6 (an integer) must appear as a point on the x-axis, 4 + 1 = 5 points will be needed. This divides the x-axis into the points 3.0, 4.0, 5.0, 6.0, and 7.0.
Fractional values, however, are more difficult. In general, if you can isolate the fractional part (and this evenly divides the range), the maximum number of points needed is given by this formula: