Package com.singularsys.jep.walkers

Class SubstitutionVisitor

java.lang.Object
com.singularsys.jep.walkers.DoNothingVisitor
com.singularsys.jep.walkers.SubstitutionVisitor
All Implemented Interfaces:
JepComponent, ParserVisitor, Serializable
public class SubstitutionVisitor extends DoNothingVisitor
Allows substitution of variable with values or expressions. For example 
 Jep jep = new Jep();
 SubstitutionVisitor sv = new SubstitutionVisitor(jep);
 Node node = jep.parse("x^2+x");
 Node sub = jep.parse("sin(y)");
 Node res = sv.substitute(node,"x",sub);
Will give the expression "(sin(y))^2+sin(y)".

Various different types of substitution are available.

Substitute a variable by a value.
substitute(Node, String, Object)
Substitute a variable by an expression
substitute(Node, String, Node)
Substitute a set of variables by a set of values
substitute(Node, String[], Object[])
Substitute a set of variables by a set of expressions
substitute(Node, String[], String[])
Substitute using an expression of the form x=z+3
substitute(Node, Node)
Substitute using a set of expressions of the form x=z+3
substitute(Node, Node[])

The methods which do multiple substitutions at the same time do not apply substitutions to the expressions which have been substituted. Hence if we try to use two substitutions x=y+2, y=z+3 the result of substituting into x^2+y^2 will be (y+2)^2+(z+3)^2 and not (z+3+2)^2+(z+1)^2. This prevents possible infinite recursion. To completely substitute a set of expressions a loop could be used. 

 Node base = jep.parse("x^2+y^2");
 Node sub1 = jep.parse("x=y+2");
 Node sub2 = jep.parse("y=z+3");
 Node subs[] = new Node[] {sub1,sub2};
 for(Node sub:subs) {
    base = sv.substitute(base, sub);
 }
Note that the order of substitution matters.
Author:
Rich Morris Created on 16-Nov-2003
See Also:

  • Field Details

  • Constructor Details

    • SubstitutionVisitor

      public SubstitutionVisitor(Jep j)

    • SubstitutionVisitor

      public SubstitutionVisitor()
      Constructor to uses as a JepComponent. init(Jep) method must be called to set the jep instance.
      Since:
      3.4.0

  • Method Details

    • init

      public void init(Jep j)
      Description copied from interface: JepComponent
      Initialize the component. This method is called whenever a component is added to Jep. Hence, it allows components to keep track of the other components they may rely on.
      Specified by:
      init in interface JepComponent
      Overrides:
      init in class DoNothingVisitor
      Parameters:
      j - the current Jep instance

    • substitute

      public Node substitute(Node orig, String name, Node replacement) throws ParseException
      Substitutes all occurrences of variable var with replacement. Does not do a DeepCopy.
      Parameters:
      orig - the expression we wish to perform the substitution on
      name - the name of the variable
      replacement - the expression var is substituted for
      Returns:
      the tree with variable replace (does not do a DeepCopy)
      Throws:
      ParseException

    • substitute

      public Node substitute(Node orig, Node sub) throws ParseException
      Substitutes into orig the equation given by sub
      Parameters:
      orig - the equation to substitute into
      sub - and equation of the form x=....
      Returns:
      a copy of orig after substitution
      Throws:
      ParseException - if sub is of the wrong form

    • substitute

      public Node substitute(Node orig, Node[] subs) throws ParseException
      Substitute a set of equations into the original. For example 
       
        Node base = jep.parse("x^2+y^2");
        Node sub1 = jep.parse("x=y+2");
        Node sub2 = jep.parse("y=z+3");
        Node res = sv.substitute(base, new Node[] {sub1,sub2});
      Node this method does not do two levels of substitution, so the result here is (y+2)^2+(z+3)^2.
      Parameters:
      orig - the expression to substitute into
      subs - a set of equations of the form x=...
      Returns:
      a copy of orig after substitution
      Throws:
      ParseException

    • substitute

      public Node substitute(Node orig, String[] names, Node[] replacements) throws ParseException
      Substitutes all occurrences of a set of variables var with a set of replacements. Does not do a DeepCopy. For example 
      
	Node base = jep.parse("x^2+y^2");
	Node sub1 = jep.parse("y+2");
	Node sub2 = jep.parse("z+3");
	Node res = sv.substitute(base, new String[]{"x","y"},new Node[] {sub1,sub2});
      Node this method does not do two levels of substitution, so the result here is (y+2)^2+(z+3)^2.
      Parameters:
      orig - the expression we wish to perform the substitution on
      names - the names of the variable
      replacements - the expression var is substituted for
      Returns:
      the tree with variable replace (does not do a DeepCopy)
      Throws:
      ParseException

    • substitute

      public Node substitute(Node orig, String[] names, Object[] values) throws ParseException
      Substitute all occurrences of variables with matching name with corresponding values. For example 
      substitute(node, new String[]{"x","y"}, new Double[]{3.0,2.0});
      Parameters:
      orig - the equation to substitute into
      names - set of variable names
      values - set of values
      Returns:
      node with the substitution performed
      Throws:
      ParseException

    • substitute

      public Node substitute(Node orig, String name, Object value) throws ParseException
      Substitute a single variable with a given value. For example substitute(node, "x", 3.0);
      Parameters:
      orig - equation to perform substitution on
      name - variable name
      value - value to use
      Returns:
      node with the substitution performed
      Throws:
      ParseException
      Since:
      3.4.0

    • substitute

      public Node substitute(Node orig, String[] oldNames, String[] newNames) throws ParseException
      Renames a set of variables with a new set of names.
      Parameters:
      orig - equation to perform substitution on
      oldNames - the old variable name
      newNames - the new variable names
      Returns:
      node with the substitution performed
      Throws:
      ParseException

    • visit

      public Object visit(ASTVarNode node, Object data) throws JepException
      Description copied from class: DoNothingVisitor
      Visit a variable node. Can be overridden by subclasses.
      Specified by:
      visit in interface ParserVisitor
      Overrides:
      visit in class DoNothingVisitor
      Throws:
      JepException