R: Calculate Polynomials from Zeros or Values

poly.calc {polynom} | R Documentation

## Calculate Polynomials from Zeros or Values

### Description

Calculate either the monic polynomial with specified zeros, or the Lagrange interpolation polynomial through the (x,y) points.

### Usage

    poly.calc(x, y, tol=sqrt(.Machine$double.eps), lab=dimnames(y)[[2]])

### Arguments

`x` | numeric vector specifying either the zeros of the desired polynomial if this is the only non-missing argument, or the x-values for Lagrange interpolation.
`y` | numeric vector or matrix specifying the y-values for the Lagrange interpolation polynomial. If `y` is a matrix, `nrow(y)` must equal `length(x)`, and each column of `y` is used separately with `x`.
`tol` | An absolute value tolerance, below which coefficients are treated as zero.
`lab` | If `y` is a matrix, lab is used as the names vector for the list result.

### Details

If `y` is a matrix, the result is a list of polynomials using each column separately.

If `x` only is given, repeated zeros are allowed. If `x` and `y` are given, repeated values in the `x` vector must have identical `y` values associated with them (up to `tol`), otherwise the first y-value only is used and a warning is issued.

### Value

Either a polynomial object, or a list of polynomials, as appropriate. In the latter case the object is of class `"polylist"`.

### See Also

`polynomial`

### Examples

    poly.calc(rep(1,3))
    ## -1 + 3*x - 3*x^2 + x^3
    poly.calc(0:4, (0:4)^2 + 1)
    ## 1 + x^2
    poly.calc(0:4, cbind(0:4, (0:4)^2 + 1), lab = letters[1:2])
    ## List of polynomials:
    ## $a:
    ## x
    ##
    ## $b:
    ## 1 + x^2

[Package polynom version 1.3-9 Index]