poly {stats} R Documentation

## Compute Orthogonal Polynomials

### Description

Returns or evaluates orthogonal polynomials of degree 1 to degree over the specified set of points x. These are all orthogonal to the constant polynomial of degree 0. Alternatively, evaluate raw polynomials.

### Usage

poly(x, ..., degree = 1, coefs = NULL, raw = FALSE)
polym(..., degree = 1, raw = FALSE)

## S3 method for class 'poly':
predict(object, newdata, ...)

### Arguments

 x, newdata a numeric vector at which to evaluate the polynomial. x can also be a matrix. Missing values are not allowed in x. degree the degree of the polynomial coefs for prediction, coefficients from a previous fit. raw if true, use raw and not orthogonal polynomials. object an object inheriting from class "poly", normally the result of a call to poly with a single vector argument. ... poly, polym: further vectors. predict.poly: arguments to be passed to or from other methods.

### Details

Although formally degree should be named (as it follows ...), an unnamed second argument of length 1 will be interpreted as the degree.

The orthogonal polynomial is summarized by the coefficients, which can be used to evaluate it via the three-term recursion given in Kennedy & Gentle (1980, pp. 343–4), and used in the “predict” part of the code.

### Value

For poly with a single vector argument:
A matrix with rows corresponding to points in x and columns corresponding to the degree, with attributes "degree" specifying the degrees of the columns and (unless raw = TRUE) "coefs" which contains the centering and normalization constants used in constructing the orthogonal polynomials. The matrix has given class c("poly", "matrix").
Other cases of poly and polym, and predict.poly: a matrix.

### Note

This routine is intended for statistical purposes such as contr.poly: it does not attempt to orthogonalize to machine accuracy.

### References

Chambers, J. M. and Hastie, T. J. (1992) Statistical Models in S. Wadsworth & Brooks/Cole.

Kennedy, W. J. Jr and Gentle, J. E. (1980) Statistical Computing Marcel Dekker.