Graphical Function Explorer (GFE)

Operating instructions

GFE is a free online function graphing tool that allows you to plot up to three functions on the same set of axes. In the functions you can refer to up to four independent variables that are controlled by sliders. This allows you to easily see the effect of changes since the graphs change in real time as you drag the sliders.

Enter a formula into one of the three input boxes ( f(x), g(x), or h(x) ), then press GRAPH or the keyboard Enter key. For example:

Press Clear, then in the top function box (f(x)) enter "cos(x)" then press GRAPH or the Enter key on the keyboard. The function will be plotted in the window above.

The syntax rules are the same as for the typed-in expressions for the Math/Scientific Calculator.

Arithmetic Operators

Function Typed in
Add +
Subtract -
Multiply *
Divide /
Exponent ^

Built-in functions

GFE has the following built-in functions. The function names are not case sensitive. Example: sin(x) is the same as Sin(x). All trigonometric functions operate in radians.

Function Example Description
Sine sin(x) The trigonometry sine function, x in radians.
Cosine cos(x) The trigonometry cosine function, x in radians.
Tangent tan(x) The trigonometry tangent function, x in radians.
Secant sec(x) The trigonometry secant function, x in radians.
Cosecant csc(x) The trigonometry cosecant function, x in radians.
Cotangent cot(x) The trigonometry cotangent function, x in radians.
Arc Sine asin(x) The angle in radians whose sine is x.
Arc Cosine acos(x) The angle in radians whose cosine is x.
Arc Tangent atan(x) The angle in radians whose tangent is x.
Square root sqrt(x) The square root of x.
Logarithm log(x) The log base 10 of x. The power to which you must raise the 10 to get x.
Natural Log ln(x) The log base e of x. The power to which you must raise e to get x.
Exp exp(x) e (approx 2.718) raised to the power of x.
Min min(a,b) Returns a or b, whichever is smallest.
Max max(a,b) Returns a or b, whichever is largest.
Abs abs(x) Returns the absolute value of x (always positive or zero)
Pow pow(x,y) Returns x raised to the power y. pow(2,3) = 8
Round round(x) Returns x rounded off to the nearest whole number
floor floor(x) Returns the highest integer less than or equal to x
ceil ceil(x) Returns the smallest integer greater than or equal to x

Constants

There are two constants you can refer to. They are not case sensitive.
  • Pi - approximately 3.142.. See PI definition for more.
  • e - approximately 2.718..
For example you could enter sin(pi) or e^2.1

Scientific notation

Scientific notation (E.G. 1e+3 for 1000) is not supported.

Automatic multiplication

If a function (such as sin() ) is preceded by a number, GFE assumes you want to multiply them. For example 3cos(2.1) will be automatically treated as if you entered 3*cos(2.1): three times the cosine of 2.1. It will not work if the function is preceded by a variable name.

Note: This feature can mislead you. For example if you enter 1/2sin(x) GFE inserts a multiply between the 2 and the sin. Since there are no parentheses, it is executed from left to right so it sees it as one half of sin(x). You may have meant it as one over 2sin(x).

Automatic parenthesis balancing

When you press GRAPH or enter, it will automatically add enough closing parentheses to balance them. For example, if you enter 2+(sin(x it will add two extra closing parentheses so they balance and evaluate it as 2+(sin(x))    Note: This may not always produce the desired result. It is best to always enter the correct expression yourself.

Graphing inequalities

GFE can be used to plot inequalities by changing the relational operator in the pull-down menu to the left of the function. There are five possible operators:

= Equals The default. The function will be plotted as a line as usual.
<= Less than or equal The part of the plane where y is less than the function value is shaded.
< Less than As above, but the line is drawn dashed.
>= Greater than or equal The part of the plane where y is greater than the function value is shaded.
> Greater than As above, but the line is drawn dashed.

Shading color

When plotting inequalities, the "monochrome shading" checkbox can be used. If this is checked, the shaded areas for all three functions are all the same light gray. This allows you to more easily see where complex functions overlap, since the more overlap there is, the darker the shading. If left unchecked, each function is shaded in a different color.

Using the cursor

If you click on "show cursor", a thin vertical line appears. If you drag this line with the mouse, it shows the values of each function where the cursor intersects that function.

You can enter the x value for the cursor manually into the text box in the upper left. After entering a value press "Graph" or the enter key. If you enter a value that is off the graph, the cursor will not show, but the values of the functions for that x value will be displayed correctly.

Changing axis limits

At each end of the x and y axis is a box containing the end values. To change them, simply edit them in place and press GRAPH or the Enter key again.

GFE will check to ensure that the lower value is at the bottom of the y axis or the left of the x-axis. Negative number are allowed.

Note on aspect ratio

The aspect ratio (ratio of width to height) of the graph window is exactly 4:3. The initial range of values on the x and y axes are in the same ratio, so a graph of y = x will be at 45°, and circles would be round, not squashed into ellipses. However, if you change the axis limits, this may no longer be true.

Using variables

When you enter your equations, you can refer to up to four variables that are controlled by sliders. These are named a, b, c and d, and you can adjust the value of each variable by moving the slider up or down. You can also enter an exact value into the box at the top of the slider, followed by the GRAPH button or the Enter key.

For example, in the chart above, press 'reset'. Note that the first function is sin(a*x). This means that each time a point is plotted, it is the sine of the current value of x multiplied by the variable a. This variable is controlled by the a slider on the right, so as you move the slider you can see the effect of varying its value. *

You can change the range of the slider by clicking on "range" below it. A dialog will appear that allows you to set the range of each slider separately.

* If you are curious: the sine curve shown is sometimes called a sine wave. The slider a is controlling the frequency of the wave. See Sine wave.

Grid and labels

If you check the "show grid" checkbox (the default), a grid is displayed with major values labeled. Since you can alter the axis limits, GFE attempts to create approximately 10 grid lines with values that are easy to interpolate.

Full screen view

Click on "full size" under the chart window. A new window will open with a new instance of GFE in it that is as large as your monitor will allow. This can be useful in a classroom with a projector.

Note: The large version is a copy of the normal-size one. Any changes you make to the large one will not be copied back to the original when you close it.

Safari users: This will be ignored if the browser is set to block pop ups - the default in Safari. (This blocking should not strictly happen, since the pages come from the same domain).

Save chart as a link

Once you have the charts exactly as you want them, you can click on 'save as link' below the applet. This will build a link to the chart that you can paste into a web page or Word document. When you later click on that link, the chart will come up exactly as you want it immediately. Also, by pasting the address back into the browser address bar and pressing Enter, you can then save the chart as a browser bookmark or favorite.

For example, you could set up a chart with all the functions and ranges as you want them for a lecture. Then, in the lecture, by clicking on this link, the chart will come up that way immediately. You can set up an unlimited number of different charts this way.

Note: Some programs cannot handle URLs beyond a certain length. (E.G. Microsoft Word has a 256 byte limit). Certain very complex charts may produce URLs that are longer than this.

Safari users: Safari defaults to suppress popups. In theory, this should not prevent this feature working, but it does. If you do not see the dialog to get the link, adjust the browser preferences to allow popups.

You can construct these links yourself if you prefer. see 'Customizing GFE' below.

Snap to integers

By checking this box, the sliders will only stop on whole numbers.

Customizing GFE

Normally, when GFE starts up it displays a default chart. You can alter what is initially displayed by attaching parameters to the URL of the web page. You can override some or all the controls to display whatever initial chart you would like.

For instructions see Customizing the General Function Explorer (GFE). But the easiest way is to use "save as link" as described above.

Graph anomalies?

Under some conditions, a graph may seem to have errors. To learn more about this see Graphing tool limitations.

Acknowledgments

The function parser in this applet was developed by Douglas Ensley and Barbara Kaskosz.

Graphing tools on this site