Hi, On Tue, Mar 18, 2014 at 08:22:44AM -0700, Marco Streng wrote: [...] > So the choices are: > > 1) explicit conversion RR --> RIF: allow / disallow > 2) explicit conversion RIF --> RR: allow / disallow > 3) automatic coercisions: disallow / (RR-->RIF) / (RIF-->RR)
It seems there are more precise cases to consider: - How do you plan to coerce a RIF element with non-trivial diameter to a RR element ? - How do you plan to convert - from RealIntervalField(2) to RealField(100) ? - from RealIntervalField(100) to RealField(2) ? - from RealField(100) to RealIntervalField(2) ? - from RealField(2) to RealIntervalField(100) ? - How do you mix both (do you plan to deal with possible compensations between number of bits of precision of the field and the diameter of the intervals) ? For example, in which case do you allow (silent) coercion, and what should be the result of the (explicit) conversion: - RIF(-1,1) -> RR - RealIntervalField(100)(1.000000001,1.000000002)) -> RealField(2) - RealField(2)(pi) -> RIF [which diameter, which endpoints ?] - and so on As for me, - it is clear that RIF(pi) should be coerced to RR(pi) - i agree with coercing from x in RealIntervalField(a) to RealField(b) when the endpoints of x are the same in RealField(b) - i have no problem for explicit conversion from RIF(-1,1) to RR, but it should be well specified in the doc, since there is no canonical way. - i am not sure wether RIF(-1,1) should coerce to RR Is Sage able to allow a coercion from A to B, but the coercion map is not the same as the conversion map there (i mean, could the coercion be a partial map of the conversion) ? As for me, i am against RR -> RIF coercion because some Sage code (not user code) could convert from RIF to RR because of some internal multiplication, and then silently back to RIF (if the coercion RR->RIF were allowed), leading to a false sense of precision and even the experienced user will not noticing it (no none can be assumed to know all Sage source code), and will not be able to hand-check this as suggested in the comment, since not all computations are done by the user. BUT, i find the second example of tcoffee quite convincing (i am also doing some RIF stuff to understand the loss of precision along a computation), so perhaps could there be an easy way to let the user tune such a convenient coercion easily at her own risks, and a way to learn about this. Or perhaps could there be a special parent for this kind of experiments. Ciao, Thierry -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
