[R] Missing "spline_coef" DLL and Rob Hyndmans monotonic interpolator

[Paul.Rustomji at csiro.au]

Hello R help

I have been trying to use Rob Hyndman's monotonically increasing spline
function.  But like another user or two seem have a problem with a
missing DLL (namely "spline_coef").  None of the previous help postings
seemed to have any solutions to this problem.  As per a Ripley
suggestion I have deleted all previous versions of R and reinstalled R
2.7.0 and the problem persists.

Thanks

Paul.

x <- seq(0,4,l=20) 
 
y <- sort(rnorm(20)) 
 
plot(x,y) 
lines(spline(x, y, n = 201), col = 2) # Not necessarily monotonic
lines(cm.spline(x, y, n = 201), col = 3)
>Error in .C("spline_coef", method = as.integer(method), n = nx, x = x,
: 
        C symbol name "spline_coef" not in DLL for package "stats"


Cm.spline code from
http://www-personal.buseco.monash.edu.au/~hyndman/Rlibrary/interpcode.R


#######################################

cm.spline <- function (x, y = NULL, n = 3 * length(x), method = "fmm",
    xmin = min(x), xmax = max(x), gulim=0)
# modification of stats package spline to produce co-monotonic
# interpolant by Hyman Filtering. if gulim!=0 then it is taken as the
upper
# limit on the gradient, and interpolant is gradient limited rather than
# monotonic. Modifications from R stats package spline()
# (c) Simon N. Wood & Rob J. Hyndman. 2002.
{
    x <- xy.coords(x, y)
    y <- x$y
    x <- x$x
    nx <- length(x)
    method <- match(method, c("periodic", "natural", "fmm"))
    if (is.na(method))
        stop("spline: invalid interpolation method")
    dx <- diff(x)
    if (any(dx < 0))
    {
        o <- order(x)
        x <- x[o]
        y <- y[o]
    }
    if(any(diff(y)<0))
        stop("Data are not monotonic")
    if (method == 1 && y[1] != y[nx])
    {
        warning("spline: first and last y values differ - using y[1] for
both")
        y[nx] <- y[1]
    }
    z <- .C("spline_coef", method = as.integer(method), n = nx,
        x = x, y = y, b = double(nx), c = double(nx), d = double(nx),
        e = double(if (method == 1) nx else 0), PACKAGE = "stats")
    z$y <- z$y-z$x*gulim  # trick to impose upper
    z$b <- z$b-gulim      # limit on interpolator gradient
    z <- hyman.filter(z)  # filter gradients for co-monotonicity
    z$y <- z$y+z$x*gulim  # undo trick
    z$b <- z$b+gulim      # transformation
    z <- spl.coef.conv(z) # force other coefficients to consistency
    u <- seq(xmin, xmax, length.out = n)
    .C("spline_eval", z$method, nu = length(u), x = u, y = double(n),
        z$n, z$x, z$y, z$b, z$c, z$d, PACKAGE = "stats")[c("x","y")]
}

cm.splinefun <- function(x, y = NULL, method = "fmm",gulim=0) 
# modification of stats package splinefun to produce co-monotonic 
#interpolant by Hyman Filtering. if gulim!=0 then it is taken as the
upper
#limit on the gradient, and intrpolant is gradient limited rather than 
# monotonic. Modifications from R stats package splinefun() 
# (c) Simon N. Wood 2002 
{ 
    x <- xy.coords(x, y)
    y <- x$y
    x <- x$x
    n <- length(x)
    method <- match(method, c("periodic", "natural", "fmm"))
    if (is.na(method)) 
        stop("splinefun: invalid interpolation method")
    if (any(diff(x) < 0)) 
    {
        z <- order(x)
        x <- x[z]
        y <- y[z]
    }
    if(any(diff(y)<0))
        stop("Data are not monotonic")
    if (method == 1 && y[1] != y[n]) 
    {
        warning("first and last y values differ in spline - using y[1]
for both")
        y[n] <- y[1]
    }
    z <- .C("spline_coef", method = as.integer(method), n = n, 
            x = as.double(x), y = as.double(y), b = double(n), c =
double(n),
            d = double(n), e = double(if (method == 1) n else 0),
PACKAGE = "stats")
    z$y <- z$y-z$x*gulim  # trick to impose upper
    z$b <- z$b-gulim      # limit on interpolator gradient
    z <- hyman.filter(z)  # filter gradients for co-monotonicity
    z$y <- z$y+z$x*gulim  # undo trick 
    z$b <- z$b+gulim      # transformation
    z <- spl.coef.conv(z) # force other coefficients to consistency
    rm(x, y, n, method)
    function(x) 
    {
        .C("spline_eval", z$method, length(x), x = as.double(x), y =
double(length(x)), 
                z$n, z$x, z$y, z$b, z$c, z$d, PACKAGE = "stats")$y
    }
}

spl.coef.conv <- function(z)
# takes an object z containing equally lengthed arrays
# z$x, z$y, z$b, z$c, z$d defining a cubic spline interpolating
# z$x, z$y and forces z$c and z$d to be consistent with z$y and
# z$b (gradient of spline). This is intended for use in conjunction
# with Hyman's monotonicity filter.
# Note that R's spline routine has s''(x)/2 as c and s'''(x)/6 as d.
# (c) Simon N. Wood
{
    n <- length(z$x)
    h <- z$x[2:n]-z$x[1:(n-1)]
    y0 <- z$y[1:(n-1)];y1 <- z$y[2:n]
    b0 <- z$b[1:(n-1)];b1 <- z$b[2:n]
    cc <- -(3*(y0-y1)+(2*b0+b1)*h)/h^2
    c1 <- (3*(y0[n-1]-y1[n-1])+(b0[n-1]+2*b1[n-1])*h[n-1])/h[n-1]^2
    dd <- (2*(y0-y1)/h+b0+b1)/h^2
    d1 <- dd[n-1]
    z$c <- c(cc,c1);z$d <- c(dd,d1)
    z
}

hyman.filter <- function(z) 
# Filters cubic spline function to yield co-monotonicity in accordance
# with Hyman (1983) SIAM J. Sci. Stat. Comput. 4(4):645-654, z$x is knot
# position z$y is value at knot z$b is gradient at knot. See also
# Dougherty, Edelman and Hyman 1989 Mathematics of Computation
# 52: 471-494. (c) Simon N. Wood
{
    n <- length(z$x)
    ss <- (z$y[2:n]-z$y[1:(n-1)])/(z$x[2:n]-z$x[1:(n-1)])
    S0 <- c(ss[1],ss)
    S1 <- c(ss,ss[n-1])
    sig <- z$b
    ind <- (S0*S1>0)
    sig[ind] <- S1[ind]
    ind <- (sig>=0)
    if(sum(ind)) 
        z$b[ind] <-
pmin(pmax(0,z$b[ind]),3*pmin(abs(S0[ind]),abs(S1[ind])))
    ind <- !ind
    if(sum(ind)) 
        z$b[ind] <-
pmax(pmin(0,z$b[ind]),-3*pmin(abs(S0[ind]),abs(S1[ind])))
    z
}





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Paul Rustomji
Rivers and Estuaries
CSIRO Land and Water
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