Matthias Schabel writes:
In building probability and likelihood models, I often encounter the issue of transforming from either to their logarithms and vice versa. Code would be much simpler and less error-prone if the appropriate domain was defined, the natural arithmetic operators were used, and the conversions occurred (or could be prevented to catch errors) as necessary, but without necessarily requiring explicit bookkeeping to distinguish these quantities and their logarithms.
This suggests a (small) set of types with appropriate conversions, much as in the units library. However, probabilities are of course unitless.
Should this idea be developed as a separate library or does it make any sense to fold it into the existing units framework?
We've tried to make mcs::units as flexible and extensible as possible in order to accommodate a wide range of value types; as you point out, since probabilities and log probabilities don't have associated units (by definition, since taking the log of a unit doesn't make any sense from a dimensional analysis standpoint), so I don't think this is something that should be directly supported in the library itself.
Voice from the back of the room: a) It might be handy, though, to have (for example) a log function that enforces unitless quantities. For example, log ( velocity * time / meters ) is fine, but if you forget to multiply by the time, you get a helpful error message. b) It might also be handy, if possible, to have some functions that take units and know what to do; for example, sqrt (m*m) properly returns meters, and so forth. < returns to lurk mode > ---------------------------------------------------------------------- Dave Steffen, Ph.D. Fools ignore complexity. Software Engineer IV Pragmatists suffer it. Numerica Corporation Some can avoid it. ph (970) 461-2000 x227 Geniuses remove it. dgsteffen@numerica.us -- Alan Perlis