# solve8quadratic: solves a degree two polynomial In rbsa: Ancillary Functions for R Programming

## Description

This function returns the root (or two roots) of the equation `ky*y + kx2*x^2 + kx*x + kk = 0`. When `dx` is not null, it is supposed to give the interval where the root lies, in that case only one root is returned.
The first parameter can be a vector of any length and all computations are vectorized.
Only real roots are considered.

## Usage

 ```1 2``` ``` solve8quadratic(y,ky,kx2,kx,kk,dx=NULL,x0=NULL,monitor=rbsa0\$monitor\$v) ```

## Arguments

 `y` Vector of values for which the equation must be satisfied. `ky` Coefficient for `y`. `kx2` Coefficient for `x^2`. `kx` Coefficient for `x`. `kk` Constant coefficient. `dx` `NULL` or the interval (`numeric(2)`) for the roots. `x0` `NULL` or a proposal in case of indetermination. `monitor` List of constants indicating the monitoring choices, see the `rbsa0\$monitor\$v` provided object as an example.

## Details

When `dx` is defined only one root is returned, belonging to the interval; if it is not possible (root(s) exist(s) and do(es) not comply) a fatal error is issued.
When every real number complies with the equation, according to available arguments, the returning value is `x0`, `mean(dx)` or `0`. When `is.null(dx)` either one or two roots is returned with `NA` when the solution is complex.

## Value

A matrix having one or two columns according to the values of `ky,kx2,kx,kk,dx`.

## Examples

 ```1 2 3 4``` ``` solve8quadratic(1:10, 1,1,0,-20); solve8quadratic( 3,-1,1,1, 1); solve8quadratic( 3,-1,1,1, 1,c(0.5,1.5)); ```

rbsa documentation built on May 31, 2017, 4:29 a.m.