On 17/01/11 18:16, Anders Logg wrote: > On Mon, Jan 17, 2011 at 06:07:19PM +0000, Garth N. Wells wrote: >> >> >> On 17/01/11 18:03, Anders Logg wrote: >>> On Mon, Jan 17, 2011 at 04:30:23PM +0000, Garth N. Wells wrote: >>>> >>>> >>>> On 17/01/11 16:28, Anders Logg wrote: >>>>> The following doesn't seem to work in Python any longer: >>>>> >>>>> A = Matrix(10, 10) >>>>> >>>>> Is matrix initialization broken? >>>>> >>>> >>>> Probably not broken - more like >>>> >>>> A = Matrix(10, 10) >>>> >>>> is not supported. Since a Matrix is in general sparse, it doesn't make >>>> sense to initialise it as above (some backends even insist on the >>>> sparsity being defined at construction). >>>> >>>> Garth >>> >>> It would be good to allow simple initialization of a Matrix without >>> requiring to go through all the hassle of creating a SparsityPattern. >>> >>> I generally don't think we should disallow certain operations just >>> because they are potentially slow. >> >> It's not just that they're slow. They cannot be supported by all backends. > > Then we throw an error. >
Better still, use an appropriate data structure ;). If a user wants a dense matrix, we should make it easy to use a dense matrix. The Matrix class in DOLFIN is sparse and the premise should be that it's distributed. Being consistent in this makes life a lot easier in parallel. >>> Some operations (like Matrix index >>> access) will only be performed for toy problems or while testing and >>> then speed is not very important (since the problem is small anyway). >>> >> >> If it's made available, it will be used. This type of operation is main >> reason for things breaking in parallel. We have getitem and setitem >> which are sufficiently unfriendly that hopefully users get the idea that >> they're for testing only. > > Just because something can be misused, it shouldn't be disallowed. > Doesn't sound like a strong argument. It should not be easy to misuse a library. That's why I can live with get/setitem, but not indexing into a sparse distributed matrix via A(i, j). > It would be easy (and more helpful) to add a message the first time > getitem/setitem is used in a program: > > Warning: Index access to matrix/vector values is potentially very > slow and it breaks in parallel. To disable this warning, set the > parameter "warning_index_access" to false. > Yes, I would like to see a set/getitem warning. Garth > -- > Anders _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
