# R-alpha: eigen

Thomas Lumley thomas@biostat.washington.edu
Mon, 11 Aug 1997 10:12:49 -0700 (PDT)

```eigen is behaving very strangely in my copy of patch 3 (solaris 2.5.1).
The calls to .Fortran are returning absolute rubbish and are also mutating
things that shouldn't be mutated.

example:
> eigen(matrix(c(1,0,0,1),2))
debug: z <- .Fortran("rs", n, n, x, values = vals, only.values == FALSE,
vectors = x, vals, vals, ierr = integer(1))
Browse[1]> x
[,1] [,2]
[1,]    1    0
[2,]    0    1
Browse[1]>
debug: if (z\$ierr) stop(paste("rs returned code ", z\$ierr, " in eigen"))
Browse[1]> dim(x)
[1] -1076060379  -977277476
Browse[1]> dim(z\$vectors)
[1] -1076060379  -977277476
Browse[1]> dim(x)<-c(2,2)
Browse[1]> dim(x)
[1] 2 2
Browse[1]> dim(z\$vectors)
[1] 2 2
Browse[1]> z\$vectors
[,1]       [,2]
[1,] 0.8506508 -0.4472136
[2,] 0.5257311  0.7236068

Not only are these clearly not the eigenvectors of the identity, but the

The problems turn out to be related: when separate objects are supplied
for each argument the function works properly, ie
z <- .Fortran("rs", n, n, x, values = vals, only.values ==  FALSE,
vectors = 0 * x, vals * 0, vals * 0, ierr = integer(1))

Somehow the arguments to .Fortran aren't getting properly copied.

Thomas Lumley
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```