[R] erf function documentation

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From: Charles Maner (ckjmaner@yahoo.com)
Date: Thu 17 Jun 2004 - 07:14:16 EST


Message-id: <20040616211416.19252.qmail@web40308.mail.yahoo.com>


Hi all. I may be wrong, (and often am), but in trying
to determine how to calculate the erf function, the
documentation for 'pnorm' states:

## if you want the so-called 'error function'
erf <- function(x) 2 * pnorm(x * sqrt(2)) - 1
## and the so-called 'complementary error function'
erfc <- function(x) 2 * pnorm(x * sqrt(2),
lower=FALSE)

Should, instead, it read:
## if you want the so-called 'error function'
erf <- function(x) 2 * pnorm(x / sqrt(2)) - 1
## and the so-called 'complementary error function'
erfc <- function(x) 2 * pnorm(x / sqrt(2),
lower=FALSE)

I've looked at a couple references and they all show
that 'x' should be divided by, not multiplied by,
'sqrt(2)'.

Again, I may be incorrect. If so, kindly let me know.
 But, if I am correct, perhaps the documentation could
be corrected in a subsequent R release.

Thanks,
Charles

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