Trap errors

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traperror(object, t)
traperror(object, MaxSteps = s)


traperror(object) traps errors produced by the evaluation of object.

traperror(object, t) does the same. Moreover, it stops the evaluation if it is not finished after a real time of t seconds.

traperror traps errors caused by the evaluation of the object. Syntactical errors, i.e., errors on parsing the object, cannot be caught. The same holds true for fatal errors causing the termination of MuPAD®.

traperror returns the error code 0 if no error happened. The error code is 1320 if the given time limit t is exceeded (“Execution time exceeded”) and 1321 if the given number of “execution steps” is exceeded. The error code is 1028 if the error was raised by the command error.

If traperror is called with a numerical second argument, this number is taken as a time limit, measured in seconds, of “process time” (see the documentation of the time function for a discussion of this term).

When using the option MaxSteps = s, the caller sets a time limit which is not system-dependent, but rather measured in terms of MuPAD evaluation steps.

The number s does not refer directly to evaluation steps, but rather to a fixed (large) number of steps which may change from one MuPAD release to the next, but is fixed within one release. The number s is twice the number of outputs caused by Pref::report(9) for a calculation using the maximum time allowed.

If traperror has no time limit set and an “Execution time exceeded” error is raised by an enclosing traperror(..., t) command, then this error is not trapped by the inner traperror. It is trapped by the traperror call that has set the time limit. Cf. Example 5.

The object can be an assignment which, for syntactical reasons, must be enclosed in additional brackets. The following code fragment demonstrates a typical application of traperror:

   if traperror((x := SomeErrorProneFunction())) = 0 then
   else RespondToTheError();

Use lasterror to reproduce the trapped error.


Example 1

Errors that happen during the execution of kernel functions have various error codes, depending on the problem. E.g., “Division by zero” produces the error code 1025:

y := 1/x: traperror(subs(y, x = 0))

Error: Division by zero. [_power]

Example 2

All errors raised using the function error have the error code 1028. Errors during the execution of library functions are of this kind:

traperror(error("My error!"))

Error: My error!

Example 3

We try to factor a polynomial, but give up after ten seconds:

traperror(factor(x^1000 + 4*x + 1), 10)

 Error: Execution time exceeded;   Evaluating:

Example 4

For use inside other routines, it is preferable to use MaxSteps instead of a time limit, to achieve consistent results across slower and faster machines:

traperror(factor(x^1000 + 4*x + 1), MaxSteps=10)

 Error: Execution MaxSteps exceeded [traperror];
  Evaluating: faclib::ddf 

Note that evaluation steps may take vastly different amounts of time, so even on the same machine, different expressions evaluated with the same value of MaxSteps may be terminated after very different lengths of time:

time(traperror(factor(x^1000 + 4*x + 1), MaxSteps=1));
time(traperror(while TRUE do 1 end_while, MaxSteps=1));
time(traperror(int(1/sqrt(1/r-1/r0), r=0..r0), MaxSteps=1))

Example 5

Here we have two nested traperror calls. The inner call contains an unterminated loop and the outer call has a time limit of 2 seconds. When the execution time is exceeded, this special error is not trapped by the inner traperror call. Because of the error, print(1) is never executed:

traperror((traperror((while TRUE do 1 end)); print(1)), 2)

Error: Execution time exceeded.



Any MuPAD object


The time limit: a positive integer


The execution limit: a positive integer

Return Values

Nonnegative integer.

See Also

MuPAD Functions