[Matrix-SIG] I have working code that implements active-castingconcept.

Rob W. W. Hooft rob@hooft.net
Thu, 20 Jan 2000 10:24:37 +0100 (MET)

>>>>> "TO" == Travis Oliphant <Oliphant.Travis@mayo.edu> writes:

 >> I am using some functions that use 2 arrays: a small one, used
 >> repeatedly and a big one that changes on every invocation. If the
 >> small array is passive-d and the big one is active-f, this will
 >> cast the small one to 'f' on every invocation. Without the
 >> active/passive patch, I'd find out about this inefficiency because
 >> the result would be of type 'd'. Would there be any way of warning
 >> the programmer for this kind of inefficient casting with the new
 >> code?

 TO> Let me see if I understand: You want to be able to catch that you
 TO> are casting the passive array on every function call (presumably
 TO> so you can change it and cast once)?

 TO> Right now you have to check the output type, correct?

Right now I know I have a problem when the program slows down to 0 Kelvin.
Then I start looking for a d-array that makes everything go d.

 TO> With the current changes in CVS, the result would be of type
 TO> 'active-f' which is not the type of the small input array, so you
 TO> could just check to make sure the types are the same.  What am I
 TO> missing?

You're speaking about the program checking, I used to detect the
problems using "wall-clock-profiling".

 TO> Another person wanted two "active" arrays of different types to
 TO> raise an exception, so with that change you would make both
 TO> arrays active and if they were not the same type an error would
 TO> occur.  What do you think?

That would be one way to do it, but most tricks require me to think
whenever I use a new array, and if I am thinking, I can just as well
add ",'f'" to the instantiation in the first place..... I'm trying
to catch thinkos.

Dumb alternative suggestions:

 - active=-1 means complain if you need to down-cast another array
   (i.e. non-scalar).

 - in some sort of debugging mode, keep a count of the number of times
   each array is down-casted, and raise InefficientCode("Frequent
   down-cast") if this happens often.

Don't get me wrong here: I really think your code is a great improvement,
and the point I'm raising is really of secondary importance (even to me).


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