On Tue, May 5, 2009 at 9:28 AM, Jason Grout <jason-s...@creativetrax.com> wrote: > > Paul Zimmermann wrote: >> Hi, >> >> I got the following error in a Sage program I wrote: >> >> TypeError: unsupported operand parent(s) for '*': 'Full MatrixSpace of 2 by >> 1 dense matrices over Integer Ring' and 'Full MatrixSpace of 2 by 2 dense >> matrices over Rational Field' >> >> for the following instruction: >> >> --> 152 vA = v.transpose() * invA >> >> Here, v is a vector of dimension n, and invA is a n x n matrix. >> >> In mathematics, a vector of dimension n is usually considered as a n x 1 >> matrix, thus to multiply it to the left of a n x n matrix, one has first >> to transpose it. >> >> sage: m = matrix(SR,[[a,b],[c,d]]); m >> >> [a b] >> [c d] >> >> sage: v = vector(SR, [d,e]); v >> (d, e) >> >> sage: m * v >> (a*d + e*b, c*d + e*d) >> >> sage: v.transpose() * m >> --------------------------------------------------------------------------- >> TypeError Traceback (most recent call last) >> >> /users/cacao/zimmerma/.sage/temp/patate.loria.fr/9803/_users_cacao_zimmerma_Adm_Cacao_ANC_Hadamard_algo2_sage_6.py >> in <module>() >> >> /usr/local/sage-3.4-core2/sage/local/lib/python2.5/site-packages/sage/structure/element.so >> in sage.structure.element.Matrix.__mul__ (sage/structure/element.c:11263)() >> >> /usr/local/sage-3.4-core2/sage/local/lib/python2.5/site-packages/sage/structure/coerce.so >> in sage.structure.coerce.CoercionModel_cache_maps.bin_op >> (sage/structure/coerce.c:5848)() >> >> TypeError: unsupported operand parent(s) for '*': 'Full MatrixSpace of 2 by >> 1 dense matrices over Symbolic Ring' and 'Full MatrixSpace of 2 by 2 dense >> matrices over Symbolic Ring' >> >> but v * m works: >> >> sage: v * m >> (a*d + e*c, b*d + e*d) > > When you just do v*m or m*v, m acts on the vector in the "obvious" way > (i.e., in v*m, v is considered a row vector, while in m*v, v is > considered a column vector). For me, that means I often do not have to > think about "row" versus "column" vectors. > > To further explain William's post: > > matrix(v) gives a 1xn matrix (so vectors are naturally row vectors) > > v.transpose() is the same as matrix(v).transpose(), giving an nx1 matrix > > I wish vectors were considered column vectors, but I think it's probably > too late to change that. The issue has come up before, and I imagine it > will come up again. This issue also affects the kernel, nullspace, and > other functions (which are all left kernels, left nullspaces, etc.). > Some people are working on making these functions explicit (i.e., > left_kernel/right_kernel, left_nullspace/right_nullspace, etc.).
The explicit forms like that are very nice. I try to always use them now, and really like them. I think they make code very readable. > > However, having m*v work as if v was a column vector takes care a lot of > my complaints on this issue. Having right_* functions for everything > will take care of most of the rest of my complaints. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
