variations in how long commands take

m <- matrix(1, 400, 40000)
proc.time(x0 <- apply(m, 2, sum))

[1] 21.88  3.16 40.13  0.00  0.00

So far, so good. This is more than twice as fast as the same thing in S+
6.0. But when I re-issue this command, I get:

proc.time(x0 <- apply(m, 2, sum))

[1] 37.09  4.65 63.13  0.00  0.00

proc.time(x0 <- apply(m, 2, sum))

[1] 52.34  5.44 85.29  0.00  0.00

So, my first question is: Why do the times keep going up? I first assumed that

From help(proc.time)

`proc.time' determines how much time (in seconds) the currently
  running R process already consumed.

Perhaps, you want to look to the help page of 'system.time'.


guido
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