On Sat, May 17, 2008 at 12:40 AM, kcrisman <[EMAIL PROTECTED]> wrote: > >> >> > The problem is that you can't actually mutate self into a new type. >> > The functions rescale_col/rescale_row change self, and changing the >> > basering of self is not allowed (because the storage format for >> > different baserings can be wildly different). > > This makes a LOT of sense. > >> >> > Not sure how the API should work, you'd need a function that returns >> > a copy of the matrix, in a new basering, with the row/col scaled. > > I have tried this, but there must still be some problem similar to the > above. I've modified the original > example below and show the problem. If I make it > temp.rescale_row_c(i, s, starcol) > it claims there is no method rescale_row_c, which I suppose has > something to do with how Cython interacts with Python. So does this > mean that what I am trying is simply impossible, or is there another > layer of nesting required? (I thought a function could call itself.) > I would have been surprised before, but now I'm not so sure. > >> >> I think you should just change things so that the error message is >> much much better? >> >> Anyway, now you see a good reason why making ZZ matrices over QQ >> by default is a good idea! > > This I can definitely do. But it would be nice to truly have this, > because I still (in principle) want to be able to do > sage: a = matrix(3,range(9)); type(a) > <type 'sage.matrix.matrix_integer_dense.Matrix_integer_dense> > sage: a.rescale_row(1,i/2) > and have the "correct" answer come out rather than just an error > message saying I need to change the base ring somehow. Changing the > default ring, though a fine idea, wouldn't help here.
That is impossible, since an object absolutely can't change its own type. Sorry. > > Thanks for the help - slowly I'm getting Python's nuances. > > - kcrisman > > In matrix0.pyx: > > def test(self, Py_ssize_t i, s, Py_ssize_t start_col=0): > try: > s = self._coerce_element(s) > self.rescale_row_c(i, s, start_col) > except TypeError: > temp = self.copy() > temp = temp.change_ring(Sequence([s,temp.base_ring() > (0)]).universe()) > print type(temp) > return temp.test(i, s, start_col) > > cdef rescale_row_c(self, Py_ssize_t i, s, Py_ssize_t start_col): > cdef Py_ssize_t j > for j from start_col <= j < self._ncols: > self.set_unsafe(i, j, self.get_unsafe(i, j)*s) > > sage: a=matrix(3,range(9)); a > > [0 1 2] > [3 4 5] > [6 7 8] > sage: a.temp(1, 1/2); a > <type 'sage.matrix.matrix_rational_dense.Matrix_rational_dense'> > > [0 1 2] > [3 4 5] > [6 7 8] > sage: b = a.temp(1,1/2); type(b) > <type 'sage.matrix.matrix_rational_dense.Matrix_rational_dense'> > <type 'NoneType'> > > > -- William Stein Associate Professor of Mathematics University of Washington http://wstein.org --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
