code review 6907048: math/rand: add example / regression test

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.

[rsc, 2012-12-07 15:13:00]

Hello golang-dev@googlegroups.com,

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

[bradfitz, 2012-12-07 16:30:52]

LGTM

On Fri, Dec 7, 2012 at 7:13 AM, <rsc@golang.org> 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/6907...
>
> 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]
> +}
>
>
>

[rsc, 2012-12-07 16:59:03]

*** Submitted as https://code.google.com/p/go/source/detail?r=477b2e70b12d ***

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.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/6907048

[corburn, 2012-12-08 04:19:07]

Typo: Should the Int64 in the second line of this comment be a Int63?

// 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'.

On Friday, December 7, 2012 9:59:03 AM UTC-7, rsc wrote:
>
> *** Submitted as 
> https://code.google.com/p/go/source/detail?r=477b2e70b12d *** 
>
> 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. 
>
> R=golang-dev, bradfitz 
> CC=golang-dev 
> https://codereview.appspot.com/6907048 
>
>
> https://codereview.appspot.com/6907048/ 
>

[dsymonds, 2012-12-08 08:11:34]

On Sat, Dec 8, 2012 at 3:19 PM, Jason Travis <infomaniac7@gmail.com> wrote:

> Typo: Should the Int64 in the second line of this comment be a Int63?

Yes, well spotted.