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Adding Labels, Lines and Points to Dynamic Graphs: PG Code Snippet

This code snippet shows the essential PG code to add labels, lines and points to dynamically generated graphs. Note that these are insertions, not a complete PG file. This code will have to be incorporated into the problem file on which you are working.

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PG problem file Explanation

We have no required additions to the tagging and description section of the file, and we obviously need to include PGgraphmacros.pl to do dynamic graphs.

# a graph object
$gr = init_graph(-1,-1,4,4,
size=>[400,400]); # or pixels=>[400,400]

# specify the grid manually

# or specify tickmarks
# x-axis ticks entered as y-value, color, list of x-values
# $gr->h_ticks(0,"black",1,2,3);
# y-axis ticks entered as x-value, color, list of y-values
# $gr->v_ticks(0,"black",1.5,3);

# plot a function
add_functions($gr, "4-3*e^(-x) for x in <-1,4> " .
    "using color:blue and weight:2");

# add a label
$gr->lb( new Label(0.25,3.25,'(0,3)',

# a line

# a thicker, blue line
#    (only works for WeBWorK > 2.4)

# a dashed blue line
#    (only works for WeBWorK > 2.4)

# a thicker red arrow from (0,0) to (4,1)
#    (only works for WeBWorK > 2.4;
#    also supports the 'dashed' option)

# and a point
$gr->stamps( closed_circle(0,3,'blue') );

In the initialization part of the file, we define a dynamically generated graph. Then we can add labels, lines and points to the graph.

To add labels, we use the lb method of the graph object. The argument is a new Label object, defined by an x-coordinate, y-coordinate, label text, color, and justification. The justification can be left, center or right for the left-to-right justification, and top, middle or bottom for the top-to-bottom justification.

Lines are added by moving the graph "cursor" to a point and then drawing a line to a new point. Note that the "cursor" remains at the endpoint of the line after drawing is completed, so that any line drawn thereafter without an additional moveTo method call will start at that endpoint.

And we add points by using the stamps method of the graph object. We've added a closed circle here (open_circle is also supported).

For alignment of labels, we have

  • 'left', 'center', 'right' for horizontal alignment
  • 'bottom', 'middle', 'top' for vertical alignment

For example, specifying 'left','bottom' will put the bottom left corner of the text at the specified point.

\{ image( insertGraph($gr), width=>400, 
    height=>400, tex_size=>800 ) \}

And the graph is inserted in the text portion of the problem as we'd expect any static or dynamic image to be. (Note that if we insert a graph with a smaller size than the size specified in init_graph we may want to include a note indicating that clicking on the graph will display a larger version.)

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