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From Luc Maisonobe <>
Subject [math] removing MathUserException
Date Mon, 05 Sep 2011 19:47:45 GMT

Cleaning out the ode package, I have seen that we throw ourselves a 
MathUserException when the max number of allowed evaluations was 
exceeded. I have fixed that in my local copy (not committed yet) and 
used the opportunity to replace the ad hoc code by the new Incrementor 
class, which purpose is precisely to count things and throw a dedicated 
exception (MaxCountExceededException) if needed. This also allowed to 
remove the last use of MaxEvaluationExceededException and hence the 
exception itself (which was still in the top level package).

As I wrote a few hours ago answering a question from Dennis, we can now 
get completely rid of MathUserException in the ode package. I have also 
done that and checked everything worked well. The idea behind this was 
discussed some months ago if I remember well. It was simply that users 
should better use their own unchecked exception, so they can be sure 
[math] will never catch them, when they call [math] code which itself 
call their functions back (like in ODE, root solvers, optimization ...). 
The current behavior with MathUserException was not really clean since 
we did throw it by ourselves (at least in ODE, which I removed). As an 
example, some clean user code should be:

public class Myclass implements FirstOrderDifferentialEquation {
   private static class LocalException extends RuntimeException {
     public LocalException(int a, int b, int c) {
        // store some information about a, b, c

     // some getters go here


   public void solveODE() {
      try {
          integrator.integrate(this, t0, y0, t, y);
      } catch (LocalException le) {
         // retrieve the a, b and c values


   public int getDimension() {
     return 3;

   public void computeDerivatives(double t, double[] y, double[] yDot) {

      // compute things

      if (somethingBadHappens) {
        throw new LocalException(a, b, c);


As shown in this exemple the exception is really something local to user 
code and there is a guarantee [math] will not mess with it. The user is 

I would like to finish implementing this for ODE (i.e. simply commit 
what I have already done), and to extend it to the rest of [math], 
completely removing MathUserException. I would also document this as a 
general rule for [math] users (using the example above).

What do you think ?

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