| nextn | R Documentation |
nextn returns the smallest integer,
greater than or equal to n, which can be obtained
as a product of powers of the values contained in factors.
nextn() is intended to be used to find a suitable length
to zero-pad the argument of fft
so that the transform is computed quickly.
The default value for factors ensures this.
nextn(n, factors = c(2,3,5))
n |
a vector of integer numbers (of type |
factors |
a vector of positive integer factors (at least 2 and preferably relative prime, see the note). |
a vector of the same length as n, of type
"integer" when the values are small enough (determined before
computing them) and "double" otherwise.
If the factors in factors are not relative prime,
i.e., have themselves a common factor larger than one, the result may
be wrong in the sense that it may not be the smallest integer.
E.g., nextn(91, c(2,6)) returns 128 instead of 96 as
nextn(91, c(2,3)) returns.
When the resulting N <- nextn(..) is larger than 2^53, a
warning with the true 64-bit integer value is signalled, as integers
above that range may not be representable in double precision.
If you really need to deal with such large integers, it may be advisable to use package gmp.
convolve, fft.
nextn(1001) # 1024 table(nextn(599:630)) n <- 1:100 ; plot(n, nextn(n) - n, type = "o", lwd=2, cex=1/2)
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