math/rand
Package rand
Overview
Package rand implements pseudo-random number generators.
Random numbers are generated by a Source. Top-level functions, such as Float64 and Int, use a default shared Source that produces a deterministic sequence of values each time a program is run. Use the Seed function to initialize the default Source if different behavior is required for each run. The default Source is safe for concurrent use by multiple goroutines.
For random numbers suitable for security-sensitive work, see the crypto/rand package.
Example
package main import ( "fmt" "math/rand" ) func main() { rand.Seed(42) // Try changing this number! answers := []string{ "It is certain", "It is decidedly so", "Without a doubt", "Yes definitely", "You may rely on it", "As I see it yes", "Most likely", "Outlook good", "Yes", "Signs point to yes", "Reply hazy try again", "Ask again later", "Better not tell you now", "Cannot predict now", "Concentrate and ask again", "Don't count on it", "My reply is no", "My sources say no", "Outlook not so good", "Very doubtful", } fmt.Println("Magic 8-Ball says:", answers[rand.Intn(len(answers))]) }
Example (Rand)
This example shows the use of each of the methods on a *Rand. The use of the global functions is the same, without the receiver.
package main import ( "fmt" "math/rand" "os" "text/tabwriter" ) func main() { // Create and seed the generator. // Typically a non-fixed seed should be used, such as time.Now().UnixNano(). // Using a fixed seed will produce the same output on every run. r := rand.New(rand.NewSource(99)) // The tabwriter here helps us generate aligned output. w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0) defer w.Flush() show := func(name string, v1, v2, v3 interface{}) { fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3) } // Float32 and Float64 values are in [0, 1). show("Float32", r.Float32(), r.Float32(), r.Float32()) show("Float64", r.Float64(), r.Float64(), r.Float64()) // ExpFloat64 values have an average of 1 but decay exponentially. show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64()) // NormFloat64 values have an average of 0 and a standard deviation of 1. show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64()) // Int31, Int63, and Uint32 generate values of the given width. // The Int method (not shown) is like either Int31 or Int63 // depending on the size of 'int'. show("Int31", r.Int31(), r.Int31(), r.Int31()) show("Int63", r.Int63(), r.Int63(), r.Int63()) show("Uint32", r.Uint32(), r.Uint32(), r.Uint32()) // Intn, Int31n, and Int63n limit their output to be < n. // They do so more carefully than using r.Int()%n. show("Intn(10)", r.Intn(10), r.Intn(10), r.Intn(10)) show("Int31n(10)", r.Int31n(10), r.Int31n(10), r.Int31n(10)) show("Int63n(10)", r.Int63n(10), r.Int63n(10), r.Int63n(10)) // Perm generates a random permutation of the numbers [0, n). show("Perm", r.Perm(5), r.Perm(5), r.Perm(5)) }
Index
Examples
Package files
exp.go normal.go rand.go rng.go zipf.go
func ExpFloat64Source
func ExpFloat64() float64
ExpFloat64 returns an exponentially distributed float64 in the range (0, +math.MaxFloat64] with an exponential distribution whose rate parameter (lambda) is 1 and whose mean is 1/lambda (1) from the default Source. To produce a distribution with a different rate parameter, callers can adjust the output using:
sample = ExpFloat64() / desiredRateParameter
func Float32Source
func Float32() float32
Float32 returns, as a float32, a pseudo-random number in [0.0,1.0) from the default Source.
func Float64Source
func Float64() float64
Float64 returns, as a float64, a pseudo-random number in [0.0,1.0) from the default Source.
func IntSource
func Int() int
Int returns a non-negative pseudo-random int from the default Source.
func Int31Source
func Int31() int32
Int31 returns a non-negative pseudo-random 31-bit integer as an int32 from the default Source.
func Int31nSource
func Int31n(n int32) int32
Int31n returns, as an int32, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.
func Int63Source
func Int63() int64
Int63 returns a non-negative pseudo-random 63-bit integer as an int64 from the default Source.
func Int63nSource
func Int63n(n int64) int64
Int63n returns, as an int64, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.
func IntnSource
func Intn(n int) int
Intn returns, as an int, a non-negative pseudo-random number in [0,n) from the default Source. It panics if n <= 0.
func NormFloat64Source
func NormFloat64() float64
NormFloat64 returns a normally distributed float64 in the range [-math.MaxFloat64, +math.MaxFloat64] with standard normal distribution (mean = 0, stddev = 1) from the default Source. To produce a different normal distribution, callers can adjust the output using:
sample = NormFloat64() * desiredStdDev + desiredMean
func PermSource
func Perm(n int) []int
Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n) from the default Source.
Example
package main import ( "fmt" "math/rand" ) func main() { for _, value := range rand.Perm(3) { fmt.Println(value) } // Unordered output: 1 // 2 // 0 }
func ReadSource
func Read(p []byte) (n int, err error)
Read generates len(p) random bytes from the default Source and writes them into p. It always returns len(p) and a nil error. Read, unlike the Rand.Read method, is safe for concurrent use.
func SeedSource
func Seed(seed int64)
Seed uses the provided seed value to initialize the default Source to a deterministic state. If Seed is not called, the generator behaves as if seeded by Seed(1). Seed values that have the same remainder when divided by 2^31-1 generate the same pseudo-random sequence. Seed, unlike the Rand.Seed method, is safe for concurrent use.
func Uint32Source
func Uint32() uint32
Uint32 returns a pseudo-random 32-bit value as a uint32 from the default Source.
func Uint64Source
func Uint64() uint64
Uint64 returns a pseudo-random 64-bit value as a uint64 from the default Source.
type RandSource
A Rand is a source of random numbers.
type Rand struct { // contains filtered or unexported fields }
func NewSource
func New(src Source) *Rand
New returns a new Rand that uses random values from src to generate other random values.
func (*Rand) ExpFloat64Source
func (r *Rand) ExpFloat64() float64
ExpFloat64 returns an exponentially distributed float64 in the range (0, +math.MaxFloat64] with an exponential distribution whose rate parameter (lambda) is 1 and whose mean is 1/lambda (1). To produce a distribution with a different rate parameter, callers can adjust the output using:
sample = ExpFloat64() / desiredRateParameter
func (*Rand) Float32Source
func (r *Rand) Float32() float32
Float32 returns, as a float32, a pseudo-random number in [0.0,1.0).
func (*Rand) Float64Source
func (r *Rand) Float64() float64
Float64 returns, as a float64, a pseudo-random number in [0.0,1.0).
func (*Rand) IntSource
func (r *Rand) Int() int
Int returns a non-negative pseudo-random int.
func (*Rand) Int31Source
func (r *Rand) Int31() int32
Int31 returns a non-negative pseudo-random 31-bit integer as an int32.
func (*Rand) Int31nSource
func (r *Rand) Int31n(n int32) int32
Int31n returns, as an int32, a non-negative pseudo-random number in [0,n). It panics if n <= 0.
func (*Rand) Int63Source
func (r *Rand) Int63() int64
Int63 returns a non-negative pseudo-random 63-bit integer as an int64.
func (*Rand) Int63nSource
func (r *Rand) Int63n(n int64) int64
Int63n returns, as an int64, a non-negative pseudo-random number in [0,n). It panics if n <= 0.
func (*Rand) IntnSource
func (r *Rand) Intn(n int) int
Intn returns, as an int, a non-negative pseudo-random number in [0,n). It panics if n <= 0.
func (*Rand) NormFloat64Source
func (r *Rand) NormFloat64() float64
NormFloat64 returns a normally distributed float64 in the range [-math.MaxFloat64, +math.MaxFloat64] with standard normal distribution (mean = 0, stddev = 1). To produce a different normal distribution, callers can adjust the output using:
sample = NormFloat64() * desiredStdDev + desiredMean
func (*Rand) PermSource
func (r *Rand) Perm(n int) []int
Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n).
func (*Rand) ReadSource
func (r *Rand) Read(p []byte) (n int, err error)
Read generates len(p) random bytes and writes them into p. It always returns len(p) and a nil error. Read should not be called concurrently with any other Rand method.
func (*Rand) SeedSource
func (r *Rand) Seed(seed int64)
Seed uses the provided seed value to initialize the generator to a deterministic state. Seed should not be called concurrently with any other Rand method.
func (*Rand) Uint32Source
func (r *Rand) Uint32() uint32
Uint32 returns a pseudo-random 32-bit value as a uint32.
func (*Rand) Uint64Source
func (r *Rand) Uint64() uint64
Uint64 returns a pseudo-random 64-bit value as a uint64.
type SourceSource
A Source represents a source of uniformly-distributed pseudo-random int64 values in the range [0, 1<<63).
type Source interface { Int63() int64 Seed(seed int64) }
func NewSourceSource
func NewSource(seed int64) Source
NewSource returns a new pseudo-random Source seeded with the given value. Unlike the default Source used by top-level functions, this source is not safe for concurrent use by multiple goroutines.
type Source64Source
A Source64 is a Source that can also generate uniformly-distributed pseudo-random uint64 values in the range [0, 1<<64) directly. If a Rand r's underlying Source s implements Source64, then r.Uint64 returns the result of one call to s.Uint64 instead of making two calls to s.Int63.
type Source64 interface { Source Uint64() uint64 }
type ZipfSource
A Zipf generates Zipf distributed variates.
type Zipf struct { // contains filtered or unexported fields }
func NewZipfSource
func NewZipf(r *Rand, s float64, v float64, imax uint64) *Zipf
NewZipf returns a Zipf variate generator. The generator generates values k ∈ [0, imax] such that P(k) is proportional to (v + k) ** (-s). Requirements: s > 1 and v >= 1.
func (*Zipf) Uint64Source
func (z *Zipf) Uint64() uint64
Uint64 returns a value drawn from the Zipf distribution described by the Zipf object.
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/math/rand/