I do not understand what is the idea behind this line: B=Matrix(2,2,[QPointF(1,1),QPointF(2,2),QPointF(3,0),QPointF(4,-1)])
QPointF presumably is something like a vector, right? But matrices should contain scalars. I **think** that you are either constructing the matrix B incorrectly or you need some other object like a list or something. In order to call an array of objects a matrix you must at least define a multiplication operation between these objects. Is there any meaning to QPointF(1,1)*QPointF(2,2) for instance? Maybe if you explain what the matrix B is, we will be better able to help. Finally, SymPy does not play well with objects defined outside of the library even if they have the appropriate interfaces. But we can address this problem when we get an idea of the rest of what you are trying to do. On 12 November 2012 21:21, Shriramana Sharma <samj...@gmail.com> wrote: > Hello. I'm new to SymPy. > > I am trying to implement an algorithm in Python for merging Bezier > curves from this paper: > http://cg.cs.tsinghua.edu.cn/~shimin/pdf/cad%202001_merging.pdf and in > it (after spending quite some time in understanding the mathematics, > as I am actually a humanities scholar) I have come to the point of > implementing the system of linear equations represented by eqn (15). > > The implementation *seems* quite straightforward: > > from sympy import Matrix > A = zeros ( n + 1 , n + 1 ) # n+1, since we need to iterate 0 to n > B = zeros ( n + 1, 1 ) > for i in range ( n + 1 ) : # 0 to n > B [ i ] = ( DeltaP [ i ] [ n - i ] - ( mu ** i ) * DeltaQ [ i > ] [ 0 ] ) * 2 > for l in range ( n + 1 ) : # 0 to n > A [ i, l ] = ( 1 + ( - mu ) ** ( l + i ) ) * binomCoeff ( l + i, > i ) > X = A . LUsolve ( B ) > > (where DeltaP, DeltaQ and binomCoeff are appropriately defined > previously in my program). > > However it seems that I cannot create a Matrix with any arbitrary > value type. Since I'm using PyQt for other things I chose QPointF, but > that doesn't seem to be permitted since I can't even do: > > B=Matrix(2,2,[QPointF(1,1),QPointF(2,2),QPointF(3,0),QPointF(4,-1)]) > > as I get the error: > > B=Matrix(2,2,[QPointF(1,1),QPointF(2,2),QPointF(3,0),QPointF(4,-1)]) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > File "/usr/lib/python2.7/dist-packages/sympy/matrices/matrices.py", > line 104, in __init__ > self.mat = map(lambda i: sympify(i), mat) > File "/usr/lib/python2.7/dist-packages/sympy/matrices/matrices.py", > line 104, in <lambda> > self.mat = map(lambda i: sympify(i), mat) > File "/usr/lib/python2.7/dist-packages/sympy/core/sympify.py", line > 155, in sympify > expr = parse_expr(a, locals or {}, rational, convert_xor) > File "/usr/lib/python2.7/dist-packages/sympy/parsing/sympy_parser.py", > line 111, in parse_expr > expr = eval(code, global_dict, local_dict) # take local objects in > preference > File "<string>", line 1, in <module> > AttributeError: 'Symbol' object has no attribute 'Symbol' > > I can convert the QPointF to a pair-tuple if that is acceptable, but I > am not so sure it's mathematically OK to convert it to a complex pair > i.e. x + iy (since the complex multiplication might have side effects > when sympy is trying to find the conjugate matrix in the process of > find inv(A) ???). > > Any guidance you people can provide in this regard would be most > appreciated. Thank you! > > -- > Shriramana Sharma > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to sympy@googlegroups.com. > To unsubscribe from this group, send email to > sympy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
