Kahan summation: Difference between revisions
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(→{{header|Python}}: Contrast Pythons sum()) |
(Example implementation in R, with comparison to the standard sum() implementation) |
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Decimal('10005.85987') |
Decimal('10005.85987') |
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>>> </lang> |
>>> </lang> |
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=={{header|R}}== |
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<lang> |
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> # A straightforward implementation of the algorithm |
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> kahansum <- function(x) { |
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+ ks <- 0 |
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+ c <- 0 |
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+ for(i in 1:length(x)) { |
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+ y <- x[i] - c |
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+ kt <- ks + y |
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+ c = (kt - ks) - y |
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+ ks = kt |
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+ } |
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+ ks |
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+ } |
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> # make R display more digits in the result |
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> options(digits=10) |
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> input <- c(10000.0, 3.14159, 2.71828) |
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> kahansum(input) |
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[1] 10005.85987 |
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> # compare with the standard sum() function |
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> sum(input) |
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[1] 10005.85987 |
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> # seems like R does the "right thing" |
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> # let's use the Dr. Dobbs example (http://www.drdobbs.com/floating-point-summation/184403224) |
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> input <- c(1.0, 1.0e10, -1.0e10) |
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> kahansum(input) |
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[1] 1 |
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> sum(input) |
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[1] 1 |
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> # again, R does it right |
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</lang> |
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