Saturday, May 22, 2021

LS Fit Using Orthogonal Polynomials over the Data Interval

   One can make the vectors or functions used to compute the fit coefficients more symmetrical if one defines a set of orthogonal polynomials on the interval covered by the data. The data for the 9 sets of measurements covered the interval [0,2]. We can start by setting p0=1 and letting p1=ax+b. When we integrate the product of the two polynomials over the interval [0,2] and set it equal to zero, we are left with one undetermined constant so to be more definite we can choose the coefficients so they are small integers. We then get p1=x-1. Setting p2=ax2+bx+c and setting the integrals of the products of p2 with the other two polynomials equal to zero we are again left with one undetermined coefficient which we can again set be equal to small integers. And we get 

p2=3x2-6x+2.

  Using the same formula for λ we get the following results.



The λ functions look more symmetrical but the accuracy of the fit doesn't seem to be improved.


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