VectorFieldGraph2D1
Graphing a Vector Field in the Plane
This PG code shows how to graph a vector field in the plane.
 File location in OPL: FortLewis/Authoring/Templates/VectorCalc/VectorFieldGraph2D1.pg
 PGML location in OPL: FortLewis/Authoring/Templates/VectorCalc/VectorFieldGraph2D1_PGML.pg
PG problem file  Explanation 

Problem tagging: 

DOCUMENT(); loadMacros( "PGstandard.pl", "MathObjects.pl", "PGgraphmacros.pl", "VectorField2D.pl", ); TEXT(beginproblem()); $refreshCachedImages = 1; 
Initialization:
We need to include the macros file 
Context()>variables>add(y=>"Real"); # # Create a graph canvas # $gr = init_graph(5,5,5,5,grid=>[10,10],axes=>[0,0],pixels=>[400,400]); $gr>lb('reset'); foreach my $j (1..4) { $gr>lb( new Label(4.7, $j, $j,'black','center','middle')); $gr>lb( new Label(4.7, $j,$j,'black','center','middle')); $gr>lb( new Label( $j,4.7, $j,'black','center','middle')); $gr>lb( new Label( $j,4.7,$j,'black','center','middle')); } $gr>lb( new Label(4.7,0.2,'x','black','center','middle')); $gr>lb( new Label(0.2,4.7,'y','black','center','middle')); VectorField2D( graphobject => $gr, Fx => Formula("x/(x^2+y^2)"), Fy => Formula("y/(x^2+y^2)"), xvar => "x", yvar => "y", xmin => 5, xmax => 5, ymin => 5, ymax => 5, xsamples => 10, ysamples => 10, vectorcolor => "blue", vectorscale => 1.5, vectorthickness => 2, xavoid=>0, yavoid=>0, ); 
Setup:
We create a blank graph canvas and add labels to it. Then, using the 
Context()>texStrings; BEGIN_TEXT This is a velocity vector field for an explosion at the origin that decreases in speed the farther the distance is from the origin. $PAR $BCENTER \{ image(insertGraph($gr),width=>400,height=>400,tex_size=>700) \} $ECENTER END_TEXT Context()>normalStrings; 
Main Text: 
$showPartialCorrectAnswers = 1; 
Answer Evaluation: 
Context()>texStrings; BEGIN_SOLUTION Solution explanation goes here. END_SOLUTION Context()>normalStrings; COMMENT('MathObject version.'); ENDDOCUMENT(); 
Solution: 