[R] ODE solver

[William Dunlap]

Using options(warn=2) is the easiest way to get this function to stop when
it makes the warning, but it will stop at any warning, not just the one you
are worried about.  You can use withCallingHandlers() or tryCatch() to be
more selective.  E.g., the following will stop on any warning that has "time"
in the warning message but willl print the warning message and continue
for other warnings.

catchTimeWarning <- function(expr) {
   withCallingHandlers(expr, 
            warning=function(e){
               warningMsg <- conditionMessage(e)
               if (grepl("time", warningMsg)) {
                  stop(warningMsg)
               } else {
                  message(warningMsg)
                  invokeRestart("muffleWarning")
               }
            }
   )
}

Here is an example of using it

> f <- function (n) 
{
    # naive way to compute factorial
    if (n < 1 || n != round(n)) {
        warning("This will take a very long time")
    }
    fac <- n
    while ((n <- n - 1) != 0) {
        fac <- fac * n
    }
    if (is.infinite(fac)) {
        warning("Factorial calculation overflowed")
    }
    fac
}
> catchTimeWarning(f(5))
[1] 120
> catchTimeWarning(f(1000))
Factorial calculation overflowed
[1] Inf
> catchTimeWarning(f(-1.5))
Error in function (e)  : This will take a very long time

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of David Winsemius
> Sent: Thursday, May 02, 2013 7:22 AM
> To: Tjun Kiat Teo
> Cc: r-help at r-project.org
> Subject: Re: [R] ODE solver
> 
> 
> On May 2, 2013, at 1:36 AM, Tjun Kiat Teo wrote:
> 
> > I am trying to use the  package ode and periodically it will come up with
> > this error message
> >
> > Warning..Internal T (=R1) and H (=R2) are
> > such that in the machine, T + H = T on the next step
> > (H = step size). Solver will continue anyway.
> >
> > And then the program just take very long to run. Is there anyway to get the
> > program to terminate when this warning is issued instead of continuing to
> > run ?
> 
> Standard debugging strategy: You set option to terminate when a warning is issued:
> 
> options(warn=2)
> 
> ?options # And especially review the examples
> 
> You can also arrange for R to drop back into the browser():
> 
> ?browser
> 
> --
> 
> David Winsemius
> Alameda, CA, USA
> 
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