Re: [boost] [math] pow redux and observations

From: Bruno Lalande (bruno.lalande_at_[hidden])
Date: 2008-05-29 17:58:54

Hi John,

First of all: I'd like to ensure you had my response of may 27, since
the mail system sent me today a notification saying it couldn't be
delivered...?? When I search on Gmane I can see it so I think it's OK
though...

Second: in my previous mails I used the term "policy" where I should
have used "error" since policies are rather the actions taken in case
of error. Sorry for the terminological confusion...

So finally, I think the best way is to create a new error. There are 2
options: either we call it zero_power_error and it's bound to be only
used in pow, or we call it undetermined_result_error so that it can be
eventually reused later for something else. The default policy for
this error will be ignore_error. If we choose "zero_power_error", the
result in case of ignore_error will be 1. If we choose
"undetermined_result_error", the best way is to make the result depend
on the function where it's used. In this case, the
raise_undetermined_result_error will have to take that value in
parameter. For example, in pow:

return policies::raise_undetermined_result_error<T>(
           "boost::math::pow(%1%)",
           "The result of pow<0>(%1%) is undetermined",
           base,
           T(1),  // value to return in case of ignore_error
           policy
       );

Which of the 2 options do you prefer?

For the throw_on_error policy, do you see any existing exception (std
or boost) that could fit or is it better to create a new one?
For the errno_on_error policy, how about setting errno to EDOM and
returning a NaN?

Bruno