On May 1, 2011, at 1:35 PM, Tom Bachmann wrote: > On 1 Mai, 16:40, Haz <christian.mu...@gmail.com> wrote: >> The cache issue runs deeper -- variable x, that depends on variably y, may >> simplify to something that doesn't even involve y because of the assumptions >> that come with y. In this case, a result is stored for x that is only valid >> under the right assumptions for y, and we would need to be very careful >> about what cache entries change when we delete y. >> >> The example may sound contrived, but it does arise in practice, and was a >> headache to debug. >> > > Well there must be an end to it, right? Every assumption is about > symbols. Every symbol x that depends in any way on another symbol y > has y in its free_symbols. In fact any exrpession has all symbols it > depends on (recursively) in its free_symbols. Hence it would be enough > to pull all assumptions involving any free symbols into the hash > computation. > > Right? [If not then one point in the above chain of argument must be > wrong; this is very well possible :-)] > > Of course then we want a quick way to find all assumptions involving a > given symbol. The easiest would be to have the symbol store a list of > assumptions it is involved in. … Which brings us back to ronan's > comment that all this is not much different from storing assumptions > with the symbols anyway.
Even if we were to decide that this was a good idea (I'm personally still not convinced), we also need to consider the speed implications. Hash computation should be very fast. Aaron Meurer > >> On Sat, Apr 30, 2011 at 2:21 PM, Tom Bachmann <ness...@googlemail.com>wrote: >> >> >> >>>> It should also be emphasized that it isn't just a simple notion of >>>> cleaning up assumptions after yourself -- the cache interacts in quite an >>>> intertwined way. Under the right assumptions, expressions will be >>>> simplified, and variables will be assigned certain values. If that's >>> stored >>>> in the cache, changing any related assumption will invalidate the result. >> >>> Why not make assumptions part of the hash of an object? At least to >>> the extent that the cache is concerned? >> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sympy" group. >>> To post to this group, send email to sympy@googlegroups.com. >>> To unsubscribe from this group, send email to >>> sympy+unsubscr...@googlegroups.com. >>> For more options, visit this group at >>> http://groups.google.com/group/sympy?hl=en. >> >> > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to sympy@googlegroups.com. > To unsubscribe from this group, send email to > sympy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
