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Hello uni, Originally Posted by: uni But it is possible.
P.S. This is not a correct example too, the determinant is zero. The sum of squares must be on all points. Thank you for considering this . If you include the sum of squares to your example above, then it is equivalent as finding the roots of this three equations sum(((el(pp,i)f(el(xx,i),a1,a2,a3))*diff((f(el(xx,i),a1,a2,a3)),a1)),i,1,n)≡0sum(((el(pp,i)f(el(xx,i),a1,a2,a3))*diff((f(el(xx,i),a1,a2,a3)),a2)),i,1,n)≡0sum(((el(pp,i)f(el(xx,i),a1,a2,a3))*diff((f(el(xx,i),a1,a2,a3)),a3)),i,1,n)≡0It is a well known and maybe redundant to say, sorry  the first derivatives over three unknowns (a1,a2,a3) should be zero. The Jacobian of these three equations should not be zero (say, giving all xx different). The problem is in derivatives, Jacobi matrix etc. (includes summation and quite large expressions). Whenever I tried to solve this root finding problem in SMath, finding derivatives, Jacobian etc. causes the main problem. Anyway, could you please try to solve with this method the three above equations using your example function, but with more than three points. Regards, Radovan P.S. I just saw that you added smz file as well. I might try myself ass well  but have doubts that I would be successful Edited by user 04 October 2012 16:11:34(UTC)
 Reason: Not specified 
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!" 