```help fracdydx
also see:  fracpoly
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Title

fracdydx -- Evaluate derivatives of fractional polynomials

Syntax

fracdydx [varname] [, options]

options                        Description
-------------------------------------------------------------------------
coeffs(# [#...]|matrixname)  defines the regression coefficients to be
used
deriv(#)                     order of derivative to be calculated
gen(newvarname)              stores the required derivative in
newvarname
powers(# [#...]|matrixname)  defines the fractional polynomial powers
to be used
-------------------------------------------------------------------------

Description

fracdydx evaluates derivative(s) of a fractional polynomial function at
varname (if specified) or at the xvar most recently used by fracpoly.

If powers() and coeffs() are not specified, powers and regression
coefficients from the most recent fit of fracpoly are used.  Otherwise,
powers from powers() and coefficients from coeffs() 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 the deriv()th derivative of the FP into newvarname.

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

Stored quantities

fracdydx is an R-class program and saves in the following r() locations:

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

Examples

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

Author

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

Also see

```