[R] Pass an optional argument from Fortran subroutine to a R wrapper

[Erin Hodgess]

Hello!
You can't really pass the matrix as a matrix.  Send it as a vector,
re-construct it in the Fortran program.

Actually, if it's a covariance matrix and symmetric, you may be able to get
away with just sending part of the matrix.  For example, if you have the
following:

covmat<- matrix(c(1,0.9,0.81,0.9,1,0.9,0.81,0.9,1),nrow=3,ncol=3,byrow=TRUE)

cov1 <- covmat[1:3]



Then pass cov1 as a numeric.


It's easier and faster to manipulate your covariance matrix in the Fortran
program.


Hope this helps.


Sincerely,

Erin

On Tue, Sep 6, 2016 at 2:51 PM, Kodalore Vijayan, Vineetha W <vwkv13 at mun.ca>
wrote:

> Hello,
>
> I have a Fortran subroutine which uses an optional argument in the call.
>
>     subroutine data (n,ns,alpha,covmat,x,y)
>
>     integer, intent(in):: n,ns
>     double precision, intent(in)  :: alpha
>     double precision, intent(in), optional ::covmat(n,ns)
>     double precision, intent(out) :: x(n),y(n)
>     ....
>     end subroutine data
>
> I tried the following R wrapper for this subroutine and got an error
> saying,
>
>      Error in array(x, c(length(x), 1L), if (!is.null(names(x)))
> list(names(x), :
>     'data' must be of a vector type, was 'NULL'
>
> I'm not sure if I passed the arguments correctly in the .Fortran() call. I
> couldn't find anything helpful online. I would really appreciate any
> help/comments.
>
>     data1 <- function(n,ns,alpha,covmat=NULL){
>
>     tmp <- .Fortran("data",
>     n = as.integer(n),ns= as.integer(ns)
>     alpha=as.numeric(alpha),covmat=as.matrix(covmat),
>     x=as.double(rep(0,n)),y=as.double(rep(0,n)))
>     )
>      }
>     result <- list(x=tmp$x, y=tmp$y)
>
>     return(result)
>     }
>
> Thanks,
> Vineetha
>
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>
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-- 
Erin Hodgess
Associate Professor
Department of Mathematical and Statistics
University of Houston - Downtown
mailto: erinm.hodgess at gmail.com

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