R: Create a Monomial Basis

create.monomial.basis {fda} | R Documentation

## Create a Monomial Basis

### Description

Creates a set of basis functions consisting of powers of the argument.

### Usage

    create.monomial.basis(rangeval=c(0, 1), nbasis=NULL,
             exponents=NULL, dropind=NULL, quadvals=NULL,
             values=NULL, basisvalues=NULL, names='monomial',
             axes=NULL)

### Arguments

`rangeval` | a vector of length 2 containing the initial and final values of the interval over which the functional data object can be evaluated.
`nbasis` | the number of basis functions = `length(exponents)`. Default = if(is.null(exponents)) 2 else length(exponents).
`exponents` | the nonnegative integer powers to be used. By default, these are 0, 1, 2, ..., (nbasis-1).
`dropind` | a vector of integers specifiying the basis functions to be dropped, if any. For example, if it is required that a function be zero at the left boundary when rangeval[1] = 0, this is achieved by dropping the first basis function, the only one that is nonzero at that point.
`quadvals` | a matrix with two columns and a number of rows equal to the number of quadrature points for numerical evaluation of the penalty integral. The first column of `quadvals` contains the quadrature points, and the second column the quadrature weights. A minimum of 5 values are required for each inter-knot interval, and that is often enough. For Simpson's rule, these points are equally spaced, and the weights are proportional to 1, 4, 2, 4, ..., 2, 4, 1.
`values` | a list of matrices with one row for each row of `quadvals` and one column for each basis function. The elements of the list correspond to the basis functions and their derivatives evaluated at the quadrature points contained in the first column of `quadvals`.
`basisvalues` | A list of lists, allocated by code such as vector("list",1). This field is designed to avoid evaluation of a basis system repeatedly at a set of argument values. Each list within the vector corresponds to a specific set of argument values, and must have at least two components, which may be tagged as you wish. 'The first component in an element of the list vector contains the argument values. The second component in an element of the list vector contains a matrix of values of the basis functions evaluated at the arguments in the first component. The third and subsequent components, if present, contain matrices of values their derivatives up to a maximum derivative order. Whenever function getbasismatrix is called, it checks the first list in each row to see, first, if the number of argument values corresponds to the size of the first dimension, and if this test succeeds, checks that all of the argument values match. This takes time, of course, but is much faster than re-evaluation of the basis system. Even this time can be avoided by direct retrieval of the desired array. For example, you might set up a vector of argument values called "evalargs" along with a matrix of basis function values for these argument values called "basismat". You might want too use names like "args" and "values", respectively for these. You would then assign them to `basisvalues` with code such as the following: basisobj\$basisvalues <- vector("list",1) basisobj\$basisvalues[[1]] <- list(args=evalargs, values=basismat)
`names` | either a character vector of the same length as the number of basis functions or a simple stem used to construct such a vector. For `monomial` bases, this defaults to paste('monomial', 1:nbreaks, sep=”).
`axes` | an optional list used by selected `plot` functions to create custom `axes`. If this `axes` argument is not `NULL`, functions `plot.basisfd`, `plot.fd`, `plot.fdSmooth` `plotfit.fd`, `plotfit.fdSmooth`, and `plot.Lfd` will create axes via `do.call(x$axes[[1]], x$axes[-1])`. The primary example of this uses `list("axesIntervals", ...)`, e.g., with `Fourier` bases to create `CanadianWeather` plots

### Value

a basis object with the type `monom`.

### See Also

`basisfd`, `link{create.basis}` `create.bspline.basis`, `create.constant.basis`, `create.fourier.basis`, `create.exponential.basis`, `create.polygonal.basis`, `create.power.basis`

### Examples

    ##
    ## simplest example: one constant 'basis function'
    ##
    m0 <- create.monomial.basis(nbasis=1)
    plot(m0)

    ##
    ## Create a monomial basis over the interval [-1,1]
    ##  consisting of the first three powers of t
    ##
    basisobj <- create.monomial.basis(c(-1,1), 5)
    #  plot the basis
    plot(basisobj)

    ##
    ## rangeval of class Date or POSIXct
    ##
    # Date
    invasion1 <- as.Date('1775-09-04')
    invasion2 <- as.Date('1812-07-12')
    earlyUS.Canada <- c(invasion1, invasion2)
    BspInvade1 <- create.monomial.basis(earlyUS.Canada)

    # POSIXct
    AmRev.ct <- as.POSIXct1970(c('1776-07-04', '1789-04-30'))
    BspRev1.ct <- create.monomial.basis(AmRev.ct)

[Package fda version 2.4.8 Index]