>what if i want to evaluate this dynamic formula for a
>point (for example x=3.8 , y=4.5)such that it will
>return to me f(x,y) as a float number
>what should i do?
>i'm a beginner with visad and data object please
>explain the answer to me by a code example for these
>values for x and y
Bader,
I've included a little application below that does what
you want. To run it using the data and formula you
gave in your example, type "java Eval 3.8 4.5 x+2*y" at
the command line. Note that you can provide the
program with whatever formula and whatever values of x
and y that you want.
By the way, when writing this little app, I uncovered a
bug in the visad.formula package's waitForFormula()
method. It's been fixed, but the change probably won't
appear on the VisAD FTP site for a few days. In the
meantime, you can get the updated FormulaVar.java file
from http://palm.ssec.wisc.edu/FormulaVar.java.
Alternatively, you could replace the waitForFormula()
command below with a call to Thread.sleep(500).
Let me know if you have any more questions.
Curtis
---------------
// Eval.java
import java.rmi.RemoteException;
import visad.*;
import visad.formula.*;
public class Eval {
public static void main(String[] argv)
throws VisADException, RemoteException
{
// get arguments from command line
if (argv.length < 3) {
System.out.println("Please enter three arguments: " +
"two numbers and a formula.");
System.exit(1);
}
double d1 = 0;
double d2 = 0;
try {
d1 = Double.parseDouble(argv[0]);
d2 = Double.parseDouble(argv[1]);
}
catch (NumberFormatException exc) {
System.out.println("First two arguments must be numbers.");
System.exit(2);
}
String formula = argv[2];
// create two VisAD Data objects that store floating point values
Real x = new Real(d1);
Real y = new Real(d2);
// create formula manager
FormulaManager fman = FormulaUtil.createStandardManager();
// register Data objects with formula manager
fman.setThing("x", x);
fman.setThing("y", y);
// assign formula to new variable
fman.assignFormula("f", formula);
// wait for formula to finish computing, just to be safe
fman.waitForFormula("f");
// get value of function from formula manager
Real f = (Real) fman.getThing("f");
// print out results
System.out.println("x = " + x.getValue() + ", y = " + y.getValue());
System.out.println("f(x,y) = " + formula + " = " + f.getValue());
}
}
