[R] Fortran

[Ko-Kang Kevin Wang]

Hi,

I did this a few months ago.  Suppose I have the following Fortran
subroutine:
  c A Fortran program that calculates Fibonacci Sequence.
  c Implemented by Ko-Kang Wang

  c23456789
        SUBROUTINE Fibonacci(num, a)

  c Overriding all implicit rules, i.e. undeclare all variables.
        IMPLICIT NONE

  c Declaration of Variables
        DOUBLE PRECISION num, i, fib, prev1, prev2
        CHARACTER a
        prev1 = 1
        prev2 = 0

  c When all = TRUE, follow this loop
  c This loop prints out all values in the sequence
        IF ((a .EQ. 'T') .OR. (a .EQ. 'TRUE')) THEN
        write(*,*) 1
        DO 10 i = 2, num
          fib = prev1 + prev2
          prev2 = prev1
          prev1 = fib
          write(*,*) fib
  10    CONTINUE

  c When all = FALSE, follow this loop
  c This loop only prints the last value in the sequence
        ELSEIF ((a .EQ. 'F') .OR. (a .EQ. 'FALSE')) THEN
        DO 20 i = 2, num
          fib = prev1 + prev2
          num = fib
          prev2 = prev1
          prev1 = fib
  20    CONTINUE
        RETURN
        ENDIF
        END

Note that I have indented the subtroutine by 2 spaces, so it is easier to
read in the email.  You may wish to remove the indentation.

Now, suppose that it is saves as Fibonacci.f and that you're running on
Unix/Linux, then you will want to do:
   R CMD SHLIB Fibonacci.f
this will generates two files:
   Fibonacci.so Fibonacci.o

If you're using Windows, you will need to do:
   Rcmd SHLIB Fibonacci.f
as stated in "Writing R Extensions".

The next thing is to open R and:
  # Load the compiled shared library in.
  dyn.load("Fibonacci.so")

  # Write a function that calls the Fortran subroutine.
  Fibonacci <- function(n, all = T) {
      .Fortran("fibonacci",
         ans = as.double(n),
         as.character(all))$ans
  }

  # Try it out!
  Fibonacci(10)

  Fibonacci(10, all = F)

This is just a silly example, but you get the idea... :-)

Cheers,

Kevin

------------------------------------------------
Ko-Kang Kevin Wang
Post Graduate PGDipSci Student
Department of Statistics
University of Auckland
New Zealand
www.stat.auckland.ac.nz/~kwan022


----- Original Message -----
From: "Stephen Elijah" <ilievs at lovell.econ.queensu.ca>
To: <r-help at stat.math.ethz.ch>
Sent: Saturday, October 26, 2002 1:24 PM
Subject: [R] Fortran


> Hello everybody,
> Could someone please send me a very simple example using Fortran from
> R? Say pass a value to an executable and get the result in R. Actually it
> seems it may be possible to call an *.f file ?? or I am wrong again?
> The manual is very terse on the subject.
> Thank you very much
>
> Stephen Elijah
>
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