R-beta: spline problems(?)

"A. Tsiolakidis" <tsioltas at cs.keele.ac.uk> writes:

I am a total beginner with this whole thing so please have patience!

I am trying to run an S-plus program with a certain line:
	spline(1:nrow(y), y[,1],n=100);

This crashes with:
	Error: NAs in foreign function call (arg 8)

Apparently, this is caused by the last command of spline:
	u <- seq(xmin, xmax, length.out = n)
        .C("spline_eval", z$method, length(u), x = u, y = double(n), 
                z$n, z$x, z$y, z$b, z$c, z$d)[c("x", "y")]
}

Now, I can cause that error with: spline(1:10,1:10)
So, there  is a whole class of problems for which spline refuses to
compute anything - is this the correct behaviour? E.g.,
	spline(1:10,(1:10)/2.5) #it is alright, but ...
	spline(1:10,(1:10)/2)   # this has the "NAs.." problem

Finally, I am almost sure that the y matrix in my program has quite
normal values, i.e. values that should allow for meaningful
interpolation.
Anybody knows what this all is about?

If you have the splines library installed, could you try the same
problem using interpSpline instead of spline?  The sequence for the
1:10, 1:10 example looks like
 R> library(splines)
 R> ttt <- interpSpline(y ~ x, data.frame(x = 1:10, y = 1:10) )
 R> ttt
 polynomial representation of spline for y ~ x
    constant linear   quadratic       cubic
  1        1      1  0.0000e+00 -3.3307e-16
  2        2      1 -9.9920e-16  9.9920e-16
  3        3      1  1.9984e-15 -1.4063e-15
  4        4      1 -2.2204e-15  7.4015e-16
  5        5      1  0.0000e+00  8.8818e-16
  6        6      1  2.6645e-15 -1.7764e-15
  7        7      1 -2.6645e-15  8.8818e-16
  8        8      1  0.0000e+00  8.8818e-16
  9        9      1  2.6645e-15 -8.8818e-16
 10       10      1  0.0000e+00 -8.8818e-16
 R> plot( ttt )  # produces a nice straight line plot.
 R> predict( ttt )
 $x
  [1]  1.00  1.18  1.36  1.54  1.72  1.90  2.08  2.26  2.44  2.62
 [11]  2.80  2.98  3.16  3.34  3.52  3.70  3.88  4.06  4.24  4.42
 [21]  4.60  4.78  4.96  5.14  5.32  5.50  5.68  5.86  6.04  6.22
 [31]  6.40  6.58  6.76  6.94  7.12  7.30  7.48  7.66  7.84  8.02
 [41]  8.20  8.38  8.56  8.74  8.92  9.10  9.28  9.46  9.64  9.82
 [51] 10.00

 $y
  [1]  1.00  1.18  1.36  1.54  1.72  1.90  2.08  2.26  2.44  2.62
 [11]  2.80  2.98  3.16  3.34  3.52  3.70  3.88  4.06  4.24  4.42
 [21]  4.60  4.78  4.96  5.14  5.32  5.50  5.68  5.86  6.04  6.22
 [31]  6.40  6.58  6.76  6.94  7.12  7.30  7.48  7.66  7.84  8.02
 [41]  8.20  8.38  8.56  8.74  8.92  9.10  9.28  9.46  9.64  9.82
 [51] 10.00

 attr(,"class")
 [1] "xyVector"
 R> predict( ttt, len = 100 )
 Error in predict.npolySpline(ttt, len = 100) : unused argument to function
 R> predict( ttt, nseg = 100 )
 $x
   [1]  1.00  1.09  1.18  1.27  1.36  1.45  1.54  1.63  1.72  1.81
  [11]  1.90  1.99  2.08  2.17  2.26  2.35  2.44  2.53  2.62  2.71
  [21]  2.80  2.89  2.98  3.07  3.16  3.25  3.34  3.43  3.52  3.61
  [31]  3.70  3.79  3.88  3.97  4.06  4.15  4.24  4.33  4.42  4.51
  [41]  4.60  4.69  4.78  4.87  4.96  5.05  5.14  5.23  5.32  5.41
  [51]  5.50  5.59  5.68  5.77  5.86  5.95  6.04  6.13  6.22  6.31
  [61]  6.40  6.49  6.58  6.67  6.76  6.85  6.94  7.03  7.12  7.21
  [71]  7.30  7.39  7.48  7.57  7.66  7.75  7.84  7.93  8.02  8.11
  [81]  8.20  8.29  8.38  8.47  8.56  8.65  8.74  8.83  8.92  9.01
  [91]  9.10  9.19  9.28  9.37  9.46  9.55  9.64  9.73  9.82  9.91
 [101] 10.00

 $y
   [1]  1.00  1.09  1.18  1.27  1.36  1.45  1.54  1.63  1.72  1.81
  [11]  1.90  1.99  2.08  2.17  2.26  2.35  2.44  2.53  2.62  2.71
  [21]  2.80  2.89  2.98  3.07  3.16  3.25  3.34  3.43  3.52  3.61
  [31]  3.70  3.79  3.88  3.97  4.06  4.15  4.24  4.33  4.42  4.51
  [41]  4.60  4.69  4.78  4.87  4.96  5.05  5.14  5.23  5.32  5.41
  [51]  5.50  5.59  5.68  5.77  5.86  5.95  6.04  6.13  6.22  6.31
  [61]  6.40  6.49  6.58  6.67  6.76  6.85  6.94  7.03  7.12  7.21
  [71]  7.30  7.39  7.48  7.57  7.66  7.75  7.84  7.93  8.02  8.11
  [81]  8.20  8.29  8.38  8.47  8.56  8.65  8.74  8.83  8.92  9.01
  [91]  9.10  9.19  9.28  9.37  9.46  9.55  9.64  9.73  9.82  9.91
 [101] 10.00

 attr(,"class")
 [1] "xyVector"

The splines library is available in the src/contrib section of any of
the CRAN archives.  The master CRAN site is
	      http://www.ci.tuwien.ac.at/R/contents.html

Douglas Bates                            bates at stat.wisc.edu
Statistics Department                    608/262-2598
University of Wisconsin - Madison        http://www.stat.wisc.edu/~bates/
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