FAQ
LGTM
On Fri, Dec 7, 2012 at 7:13 AM, wrote:

Reviewers: golang-dev_googlegroups.com,

Message:
Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/


Description:
math/rand: add example / regression test

This makes sure the outputs do not change for a fixed seed.
See also https://codereview.appspot.**com/6905049<https://codereview.appspot.com/6905049>
.

Please review this at https://codereview.appspot.**com/6907048/<https://codereview.appspot.com/6907048/>

Affected files:
A src/pkg/math/rand/example_**test.go


Index: src/pkg/math/rand/example_**test.go
==============================**==============================**=======
new file mode 100644
--- /dev/null
+++ b/src/pkg/math/rand/example_**test.go
@@ -0,0 +1,69 @@
+// 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 Int64
+ // 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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