R-alpha: eigen and batch

[Thomas Lumley]

On Mon, 25 Aug 1997, Jim Lindsey wrote:
> 
> eigen:
>    I started looking in the eispack C code and traced down the
> problem. In three of the four Fortran calls in eigen, (ch,rs,cg but
> not rg), the same vector (vals) is used for the return eigenvalues as
> for two or three temporary workspace vectors. This is risky
> programming at any time and leads to a catastrophe with a 586 where
> several things may be calculated at the same time. 

No, this is a bug in .Fortran.  Everything sent to C or FORTRAN code is
supposed to be a *copy* of the R object.  This is because R is allowed to
move things around in memory whenever it feels the urge, but C and FORTRAN
assume things stay fixed.  Since everything is supposed to be copied there
is no harm in using multiple copies of the same thing. 

One possible source of this bug is in naoktrim in src/main/dotcode.c
which begins
static SEXP naoktrim(SEXP s, int * len, int *naok, int *dup)
{
        SEXP value;

        if(s == R_NilValue) {
                value = R_NilValue;
                *naok = 0;
                *dup = 0;
                *len = 0;
        }
but should begin
static SEXP naoktrim(SEXP s, int * len, int *naok, int *dup)
{
        SEXP value;

        if(s == R_NilValue) {
                value = R_NilValue;
                *naok = 0;
                *dup = 1;
                *len = 0;
        }


Thomas Lumley
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