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

[Kodalore Vijayan, Vineetha W]

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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