Poly() R function from [gsl]

Polynomials

Polynomial functions as per the Gnu Scientific Library, reference manual section 6.1. These functions are defined in header file gsl_poly.h


gsl_poly(c_gsl,x)

c_gsl: Coefficients of the poynomial (c in the function definition and the GSL ref manual) starting at the constant term and ending in the highest power; see details section. This argument is called ‘c_gsl’ (and not ‘c’ ) to avoid confusion with function c()
x: input: real values

One must be careful to avoid off-by-one errors. In C idiom, the function evaluates the polynomial

c[0]+c[1]x+c[2]x^2+\ldots+c[\mathrm{len}-1]x^{\mathrm{len}-1}c[0]+c[1]+...+c[len-1]x^(len-1)

where len is the second argument of GSL function gsl_poly_eval().

The idiom would be

c[1]+c[2]x+c[3]x^2+\ldots+c[\mathrm{len}]x^{\mathrm{len}-1}.c[1]+c[2]+...+c[len]x^(len-1).

This section is work-in-progress and more will be added when I have the time/need for the other functions here.

Robin K. S. Hankin


a <- matrix(1:4,2,2)
rownames(a) <- letters[1:2]
(jj <- gsl_poly(1:3,a))

jj-(1 + 2*a + 3*a^2)  #should be small

Useful links