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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rand_test
import (
"fmt"
"math/rand"
"os"
"text/tabwriter"
)
// This test serves as an example but also makes sure we don't change
// the output of the random number generator when given a fixed seed.
// 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.
func Example() {
// 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.Int63(), r.Int63(), r.Int63())
// 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))
// Output:
// Float32 0.2635776 0.6358173 0.6718283
// Float64 0.628605430454327 0.4504798828572669 0.9562755949377957
// ExpFloat64 0.3362240648200941 1.4256072328483647 0.24354758816173044
// NormFloat64 0.17233959114940064 1.577014951434847 0.04259129641113857
// Int31 1501292890 1486668269 182840835
// Int63 3546343826724305832 5724354148158589552 5239846799706671610
// Uint32 5927547564735367388 637072299495207830 4128311955958246186
// Intn(10) 1 2 5
// Int31n(10) 4 7 8
// Int63n(10) 7 6 3
// Perm [1 4 2 3 0] [4 2 1 3 0] [1 2 4 0 3]
}
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