I got it solved. It's a type error: the matrix sing is a matrix over QQ. If its a matrix over ZZ it works fine.
but why is gcd(2,0) = 1 for 2,0 as Rationals? in my eyes its not well defined or should be the maximum of those values. greatz Am 28.12.2010 22:08, schrieb Johannes: > Hi list, > I've a very confusing problem with some simple algorithm: > > following setting: a matrix sing: > sage: sing > [ 3 0 1] > [-2 -1 -2] > [ 0 1 0] > sage: l = sings.column(2);l > (1, -2, 0) > #my algorithem, code see below: > sage: extgcd(l) > #some printoutput for debugging: > l: (1, -2, 0) > tlist: (-2, 0) > #this should not be, d = gcd(tlist) > d: 1 > l: [1, 1] > [u, v]: [0, 1] > l: (-2, 0) > [u, v]: [1, 0] > res: [0, 1, 0] > #the result: > [0, 1, 0] > #now the same but i construct the vector on my own: > sage: l = vector([1,-2,0]);l > (1, -2, 0) > sage: extgcd(l) > l: (1, -2, 0) > tlist: (-2, 0) > #here it works fine > d: 2 > l: [1, 2] > [u, v]: [1, 0] > l: (-2, 0) > [u, v]: [1, 0] > res: [1, 0, 0] > #getting the expected result: > [1, 0, 0] > > the code of my algorithm: > > def extgcd(l): > print "l: " + str(l) > assert len(l) > 1 > > if len(l) == 2: > #calculated ext euclidean for two values > a = l[0] > b = l[1] > > u=t=1 > v=s=0 > while b>0: > q=a//b > a, b = b, a-q*b > u, s = s, u-q*s > v, t = t, v-q*t > print "[u, v]: " + str([u, v]) > return [u, v] > else: > > #this is the part where it does not work! > tlist = l[1:] > print "tlist: " + str(tlist) > d = gcd(tlist) > print "d: " + str(gcd(tlist)) > > #calculate part decomp > u, v = extgcd([l[0],d]) > #calculate rest > ttlist = extgcd(tlist) > res = [u] > #combine results > res.extend([v * item for item in ttlist]) > print "res: " + str(res) > return res > > I hope somebody can help me. > greatz Johannes > -- 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
