(This article was first published on Dan Kelley Blog/R, and kindly contributed to Rbloggers)
Introduction
As was expected, the runderiv()
function has been both useful and deficient. Useful because it offers a good replacement for smooth.spline()
calculations of derivatives for things like N^2. And deficient because it only calculated derivatives, not values!
Both an extension and a renaming were called for. The result is runlm()
.
Tests
Below are the examples from its manpage, with the results.
Case 1

library(oce)

## Loading required package: methods
## Loading required package: mapproj
## Loading required package: maps

x < 1:100
y < 1 + x/100 + sin(x/5)
yn < y + rnorm(100, sd = 0.1)
L < 4
calc < runlm(x, y, L = L, deriv = 0)
plot(x, y, type = "l", lwd = 7, col = "gray")
points(x, yn, pch = 20, col = "blue")
lines(x, calc, lwd = 2, col = "red")

Case 2

data(ctd)
plot(ctd, which = "N2")
rho < swRho(ctd)
z < swZ(ctd)
zz < seq(min(z), max(z), 0.1)
N2 < 9.8/mean(rho) * runlm(z, rho, zz, deriv = 1)
lines(N2, zz, col = "red")
legend("bottomright", lwd = 2, bg = "white", col = c("black", "red"), legend = c("swN2()",
"using runlm()"))

Comments

The fit in Case 1 is almost spookily good.

The N^2 results suggest including this as a method for
swN2()
, perhaps the default method, but that’s for another day.
Resources
 Source code: 20140411runlm.R
To leave a comment for the author, please follow the link and comment on their blog: Dan Kelley Blog/R.
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