that sounds comprehensibly. explains some more errormessages i got a few times (like 'bool has no attribute len' when using solve)
greatz Am 18.07.2011 16:54, schrieb luisfe: > For me it looks like: > > In solve, when writting a == b you assume that a and b are expressions > involving several variables. If a and b are expressions, then a == b > is also an expression. > > However, p and x*p1+y*p2 are NOT expressions, but vectors. And > equality of vectors is not the same as equality of expressions > > sage: x == y > x == y > sage: type(_) > <type 'sage.symbolic.expression.Expression'> > sage: vector([x]) == vector([y]) > False > sage: type(_) > <type 'bool'> > > So, in fact, you are passing the following command: > > sage: [x * p1 + y * p2 == p] > [False] > > sage: solve([False],x,y) > > Which has no solution. It is subtle, but I would not consider it a > bug. If you really want to use solve, you may try the following: > > sage: solve(x * p1 + y * p2 - p,x,y) > [[x == (1/4), y == (3/4)]] > > In this case, the input is a vector, that is an iterable, so solve > extracts its components and equals them to zero. > > Being said that, I recommend you to use the linear algebra > interpretation that I suggested, since it will probably be much more > efficient. > -- 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
