On Tuesday, January 18, 2011 10:19:58 AM UTC-7, einek wrote: > > Hi tvn, > > Am Montag, den 17.01.2011, 14:22 -0800 schrieb tvn: > > I try to solve for 3 variables x y z with 3 equations as below , > > I am expecting something like z = r1, x = -r1, y = -2*r1 but instead > > get x = y = z = 0 (which trivially valid though not expected). Is > > this because the numbers used too complex (equation 2) and have some > > rounding errors ? if not what's the cause and how to get around it ? > > Thanks > > > > > > > > > > sage version 4.6.1 > > > > > > solve([x + 0.106*y + 1.212*z == 0, 3.8759765625*x + 0.04801171875*y + > > 3.972*z == 0, 3.0625*x + 0.09325*y + 3.249*z == 0],[x,y,z]) > > [[x == 0, y == 0, z == 0]] #not expected > sage: A = matrix([[1, 0.106, 1.212], [3.8759765625, 0.04801171875, > 3.972], [3.0625, 0.09325, 3.249]]) > sage: A.rank() > 3 > > Thus (0,0,0) is the unique solution of your system. > > x=1,y=2,z=-1 is another solution (in fact there are many solutions for this linear system of equations) .
Cheers, > > Eckhard > > > > > > > > > > > Is this due to rounding/precision error because if I replace the 2nd > > equation with another one then it works fine ? > > > > > > solve([x + 0.106*y + 1.212*z == 0, 2.25*x + 0.841*y + 3.932*z == 0, > > 3.0625*x + 0.09325*y + 3.249*z == 0],[x,y,z]) > > [[x == -r44, y == -2*r44, z == r44]] #expected > > > > > > > > -- > > To post to this group, send email to [email protected] > > To unsubscribe from this group, send email to sage-support > > [email protected] > > For more options, visit this group at > > http://groups.google.com/group/sage-support > > URL: http://www.sagemath.org > -- > Service für Mathematik und Simulation > Dr. Eckhard Kosin, selbständiger Diplom-Mathematiker > > Am Nymphenbad 14 > D-81245 München, Germany > > Tel.: (+49)(+89) 88 88 479 > Tel.,Fax: (+49)(+89) 835 844 > mailto:[email protected] > http://www.mathematik-service-kosin.de > > -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
