{smcl} {* *! version 1.2.1 20jan2011}{...} {cmd:help fracdydx} {right:also see: {help fracpoly}} {hline} {title:Title} {p2colset 5 17 19 2}{...} {p2col :{hi:fracdydx} {hline 2}}Evaluate derivatives of fractional polynomials{p_end} {p2colreset}{...} {title:Syntax} {p 8 16 2}{cmd:fracdydx} [{varname}] [{cmd:,} {it:options}] {synoptset 29 tabbed}{...} {synopthdr} {synoptline} {synopt :{opt c:oeffs(# [#...]|matrixname)}}defines the regression coefficients to be used{p_end} {synopt :{opt d:eriv(#)}}order of derivative to be calculated{p_end} {synopt :{opt g:en(newvarname)}}stores the required derivative in {it:newvarname}{p_end} {synopt :{opt p:owers(# [#...]|matrixname)}}defines the fractional polynomial powers to be used{p_end} {synoptline} {p2colreset}{...} {title:Description} {pstd} {cmd:fracdydx} evaluates derivative(s) of a fractional polynomial function at {it:varname} (if specified) or at the xvar most recently used by {help fracpoly}. {pstd} If {opt powers()} and {opt coeffs()} are not specified, powers and regression coefficients from the most recent fit of {cmd:fracpoly} are used. Otherwise, powers from {opt powers()} and coefficients from {opt coeffs()} are used. {title:Options} {phang} {opt coeffs(# [#...] | matrixname)} defines the regression coefficients for the fractional polynomial model to be used. {phang} {opt deriv(#)} specifies the order of derivative to be calculated. Default {it:#} is 1. {phang} {opt gen(newvarname)} puts the {opt deriv()}th derivative of the FP into {it:newvarname}. {phang} {opt powers(# [#...] | matrixname)} defines the fractional polynomial powers to be used. {title:Stored quantities} {pstd} {cmd:fracdydx} is an R-class program and saves in the following {cmd:r()} locations: {cmd:r(powers)} powers for the FP representing the {cmd:deriv()}th derivative {cmd:r(coeffs)} regression coefficents for the FP representing the {cmd:deriv()}th derivative {title:Examples} {phang2}{cmd:. fracdydx}{p_end} {phang2}{cmd:. fracdydx, gen(d1)}{p_end} {phang2}{cmd:. fracdydx x, powers(-1 2) coeffs(1.25 0.65) deriv(2)}{p_end} {title:Author} {pstd} Patrick Royston, MRC Clinical Trials Unit, London, UK. ({browse "mailto:patrick.royston@ctu.mrc.ac.uk":pr@ctu.mrc.ac.uk}) {title:Also see} {psee} Manual: {manlink R fracpoly}