// 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] }