R-beta: spline problems(?)

Martin Maechler maechler at stat.math.ethz.ch
Tue Apr 7 09:54:40 CEST 1998

>>>>> "Jim" == Jim Lindsey <jlindsey at luc.ac.be> writes:

    Jim> I suspect that this is a problem that I pointed out some time ago
    Jim> with integers. seq and : produce integers and the C code of spline
    Jim> is expected doubles. Try as.double() around your 1:nrow(y) and
    Jim> seq() calls to see if the problem goes away.  Jim

Jim, this was exactly my own first suspicion, also.
But it's wrong.

spline(.) uses  xy.coord(.)  
	[[a very useful thing!  use it in your own functions!!]]
and xy.coord(.)
ends in
        return(list(x = as.real(x), y = as.real(y), xlab = xlab, 
                ylab = ylab))

which ensures that integers are coerced to real (== double in R).

It must be rather another problem, as  Ross already mentioned,
and is investigating himself.


    Tasos>  Hi,
    Tasos> I am a total beginner with this whole thing so please have patience!
    Tasos> I am trying to run an S-plus program with a certain line:
    Tasos> spline(1:nrow(y), y[,1],n=100);
    Tasos> This crashes with: Error: NAs in foreign function call (arg 8)
    Tasos> Apparently, this is caused by the last command of spline: u <-
    Tasos> seq(xmin, xmax, length.out = n) .C("spline_eval", z$method,
    Tasos> length(u), x = u, y = double(n), z$n, z$x, z$y, z$b, z$c,
    Tasos> z$d)[c("x", "y")] }
    Tasos> Now, I can cause that error with: spline(1:10,1:10) So, there is a
    Tasos> whole class of problems for which spline refuses to compute anything
    Tasos> - is this the correct behaviour? E.g., spline(1:10,(1:10)/2.5) #it
    Tasos> is alright, but ...  spline(1:10,(1:10)/2) # this has the "NAs.."
    Tasos> problem
    Tasos> Finally, I am almost sure that the y matrix in my program has quite
    Tasos> normal values, i.e. values that should allow for meaningful
    Tasos> interpolation.  Anybody knows what this all is about?
    Tasos> Thanks,
    Tasos> Tasos T.
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