help fracdydxalso see: fracpoly -------------------------------------------------------------------------------

Title

fracdydx-- Evaluate derivatives of fractional polynomials

Syntax

fracdydx[varname] [,options]

optionsDescription -------------------------------------------------------------------------coeffs(#[#...]|matrixname)defines the regression coefficients to be usedderiv(#)order of derivative to be calculatedgen(newvarname)stores the required derivative innewvarnamepowers(#[#...]|matrixname)defines the fractional polynomial powers to be used -------------------------------------------------------------------------

Description

fracdydxevaluates derivative(s) of a fractional polynomial function atvarname(if specified) or at the xvar most recently used by fracpoly.If

powers()andcoeffs()are not specified, powers and regression coefficients from the most recent fit offracpolyare used. Otherwise, powers frompowers()and coefficients fromcoeffs()are used.

Options

coeffs(#[#...]|matrixname)defines the regression coefficients for the fractional polynomial model to be used.

deriv(#)specifies the order of derivative to be calculated. Default#is 1.

gen(newvarname)puts thederiv()th derivative of the FP intonewvarname.

powers(#[#...]|matrixname)defines the fractional polynomial powers to be used.

Stored quantities

fracdydxis an R-class program and saves in the followingr()locations:

r(powers)powers for the FP representing thederiv()th derivativer(coeffs)regression coefficents for the FP representing thederiv()th derivative

Examples

. fracdydx. fracdydx, gen(d1). fracdydx x, powers(-1 2) coeffs(1.25 0.65) deriv(2)

AuthorPatrick Royston, MRC Clinical Trials Unit, London, UK. ( pr@ctu.mrc.ac.uk)

Also see