[Rd] Fortran coding standards

[Prof Brian Ripley]

On Wed, 11 Apr 2007, Vivek Rao wrote:

> I have some comments on the Fortran code in the
> fseries package in file 4A-GarchModelling.f ,
> especially the subroutine GARCHFIT and function
> DSNORM.
> I appended the code to the end of an earlier message,
> but it was rejected by some rule. Let me first say
> that I am grateful that packages for financial
> econometrics exist in R.

Please pass those on to the maintainer.

Note that currently we expect only Fortran 77 to be used in R and 
(preferably) its packages, as there still are users with a Fortran 77 
compiler and nothing later.  One major group are those on Windows, and it 
is hoped that that will move to gcc 4.2.x in 2007.  There are still quite 
a few users on OSes that are two or more years old and for which
gcc3 is the norm.

> Fortran 77 had PARAMETERs, and PARAMETERs equal to
> 99999 and 200 should have been defined instead of
> repeatedly using "magic numbers". More importantly,
> the code will fail if NN exceeds 99999, but the code
> does not check for this. I hope someone will fix this.
>
> In the code dsged the variables half, one, two should
> be made parameters, and instead of
>
>      IMPLICIT DOUBLE PRECISION (A-H, O-Z)
>
>      IMPLICIT NONE
>
> should be used and all variables declared. Although
> IMPLICIT NONE is not standard Fortran 77, it is
> standard Fortran 90 and is supported by g77.
> Experienced Fortranners know that IMPLICIT NONE
> catches errors. Another defect is the use of specific
> intrinsic functions such as DSQRT. There is no need to
> use this, since the SQRT function is generic, handling
> both single and double precision arguments.
>
> Maybe there should R coding standards to address such
> issues. I hope that eventually the Fortran code in R
> will use the modern features of Fortran 90 and later
> standards, using the gfortran compiler. However, with
> a little effort one can still write clean code in
> Fortran 77 that also conforms to later standards.

The Fortran code in R itself is (entirely, I think) imported from 
elsewhere, e.g. from EISPACK or LAPACK or Netlib.  We have little interest 
in changing long-established code, and as the recent thread 'eigen in 
beta' shows, everytime we update such code someone thinks there is a new 
bug in R.

The developer.r-project.org has a collection of references to encourage 
'portable programming', including on Fortran standards.

> Vivek Rao

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595