On Monday, March 14, 2011 9:02:48 PM UTC-7, Justin C. Walker wrote: > > Hi, and Welcome, > > On Mar 14, 2011, at 20:14 , Ben123 wrote: > > > Hello. I'm a new user to Sage. I am trying to create a matrix without > > knowing the values when it is initialized. All the examples I see have > > static matrices like > > A = matrix(QQ,2,2,[2,1,1,2]) > > My goal is to create a 2x2 matrix which I can then give values for > > later > > A[1][1]=5 > > That is correct, although I am at a loss to explain why that's how it is. > > With your matrix, > sage: A[1] > (1, 2) > > so clearly, the rows are "tuples", which are immutable. >
sage: A[1] (1, 2) sage: type(A[1]) <type 'sage.modules.vector_rational_dense.Vector_rational_dense'> sage: A[1].is_immutable() True So A[1] is a row vector, and those are immutable. Trying to set A[1][1] is trying to modify an entry of this vector. > Not all is lost, though: > > sage: A[1,1]=5 > sage: A > [2 1] > [1 5] > According to <http://sagemath.org/doc/reference/sage/matrix/docs.html>, this seems to be the right way to change an entry of a matrix. There seems to be generally helpful information in that documentation. > Perhaps someone with a closer understanding of the implementation can > explain the details. > > HTH. > > Justin > > -- > Justin C. Walker, Curmudgeon-At-Large > Institute for the Enhancement of the Director's Income > -------- > When LuteFisk is outlawed, > Only outlaws will have LuteFisk > Would this be bad? -- John -- 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 URL: http://www.sagemath.org
