21 lines
868 B
R
21 lines
868 B
R
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D1tr <- function(y, x = 1)
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{
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## Purpose: discrete trivial estimate of 1st derivative.
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## ----------------------------------------------------------------------
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## Arguments: x is optional; let's say we don't like "'"
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## ----------------------------------------------------------------------
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## Author: Martin Maechler, ~ 1990
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n <- length(y)
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if(length(x) == 1)
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c(y[2] - y[1], 0.5 * (y[-(1:2)] - y[-((n-1):n)]), y[n] - y[n-1])/x
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else {
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## Here, already using non-matching apostrophes, but developer mode
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## still seems to work ..
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if(n != length(x)) stop("lengths' of x & 'y' must equal")
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if(is.unsorted(x)) stop("'x' must be sorted !")
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c(y[2] - y[1], 0.5 * (y[-(1:2)] - y[-((n-1):n)]), y[n] - y[n-1]) /
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c(x[2] - x[1], 0.5 * (x[-(1:2)] - x[-((n-1):n)]), x[n] - x[n-1])
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}
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}
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