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The following list describes all of the built-in functions that work with numbers. Optional parameters are enclosed in square brackets ([ ]):

`atan2(`

¶`y`,`x`)-
Return the arctangent of

in radians. You can use ‘`y`/`x``pi = atan2(0, -1)`’ to retrieve the value of*pi*. `cos(`

¶`x`)-
Return the cosine of

`x`, with`x`in radians. `exp(`

¶`x`)-
Return the exponential of

`x`(`e ^`

) or report an error if`x``x`is out of range. The range of values`x`can have depends on your machine’s floating-point representation. `int(`

¶`x`)-
Return the nearest integer to

`x`, located between`x`and zero and truncated toward zero. For example,`int(3)`

is 3,`int(3.9)`

is 3,`int(-3.9)`

is -3, and`int(-3)`

is -3 as well. `log(`

¶`x`)-
Return the natural logarithm of

`x`, if`x`is positive; otherwise, return NaN (“not a number”) on IEEE 754 systems. Additionally,`gawk`

prints a warning message when`x`

is negative. `rand()`

¶-
Return a random number. The values of

`rand()`

are uniformly distributed between zero and one. The value could be zero but is never one.^{44}Often random integers are needed instead. Following is a user-defined function that can be used to obtain a random nonnegative integer less than

`n`:function randint(n) { return int(n * rand()) }

The multiplication produces a random number greater than or equal to zero and less than

`n`

. Using`int()`

, this result is made into an integer between zero and`n`

- 1, inclusive.The following example uses a similar function to produce random integers between one and

`n`. This program prints a new random number for each input record:# Function to roll a simulated die. function roll(n) { return 1 + int(rand() * n) } # Roll 3 six-sided dice and # print total number of points. { printf("%d points\n", roll(6) + roll(6) + roll(6)) }

**CAUTION:**In most`awk`

implementations, including`gawk`

,`rand()`

starts generating numbers from the same starting number, or*seed*, each time you run`awk`

.^{45}Thus, a program generates the same results each time you run it. The numbers are random within one`awk`

run but predictable from run to run. This is convenient for debugging, but if you want a program to do different things each time it is used, you must change the seed to a value that is different in each run. To do this, use`srand()`

. `sin(`

¶`x`)-
Return the sine of

`x`, with`x`in radians. `sqrt(`

¶`x`)-
Return the positive square root of

`x`.`gawk`

prints a warning message if`x`is negative. Thus,`sqrt(4)`

is 2. `srand(`

[`x`]`)`

¶Set the starting point, or seed, for generating random numbers to the value

`x`.Each seed value leads to a particular sequence of random numbers.

^{46}Thus, if the seed is set to the same value a second time, the same sequence of random numbers is produced again.**CAUTION:**Different`awk`

implementations use different random-number generators internally. Don’t expect the same`awk`

program to produce the same series of random numbers when executed by different versions of`awk`

.If the argument

`x`is omitted, as in ‘`srand()`’, then the current date and time of day are used for a seed. This is the way to get random numbers that are truly unpredictable.The return value of

`srand()`

is the previous seed. This makes it easy to keep track of the seeds in case you need to consistently reproduce sequences of random numbers.POSIX does not specify the initial seed; it differs among

`awk`

implementations.

The C version of
`rand()`

on many Unix systems is known to produce fairly poor
sequences of random numbers. However, nothing requires that an
`awk`

implementation use the C `rand()`

to implement the
`awk`

version of `rand()`

. In fact, for many years,
`gawk`

used the BSD `random()`

function, which is
considerably better than `rand()`

, to produce random numbers.
From version 4.1.4, courtesy of Nelson H.F. Beebe, `gawk`

uses the Bayes-Durham shuffle buffer algorithm which considerably extends
the period of the random number generator, and eliminates short-range and
long-range correlations that might exist in the original generator.

`mawk`

uses a different seed each time.

Computer-generated random numbers really are not truly
random. They are technically known as *pseudorandom*. This means
that although the numbers in a sequence appear to be random, you can in
fact generate the same sequence of random numbers over and over again.