# Poly

##### Polynomials

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

- Keywords
- array

##### Usage

`gsl_poly(c_gsl,x)`

##### Arguments

- 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 R function`c()`

- x
input: real values

##### Details

One must be careful to avoid off-by-one errors. In C idiom, the
function evaluates the polynomial
$$c[0]+c[1]x+c[2]x^2+\ldots+c[\mathrm{len}-1]x^{\mathrm{len}-1}$$
where len is the second argument of GSL function
`gsl_poly_eval()`

.

The R idiom would be $$c[1]+c[2]x+c[3]x^2+\ldots+c[\mathrm{len}]x^{\mathrm{len}-1}.$$

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

##### References

##### Examples

```
# NOT RUN {
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
# }
```

*Documentation reproduced from package gsl, version 2.1-6, License: GPL-3*