Math.random syntax

[Robert Scheer]

Hi.

Reading about the Math.random method I saw that by default it
generates between 0 and 1. To generate numbers between a greater range
I can use these syntaxes:

x = Math.random()/10
x = Math.random()*1 0

What is the difference between the two? I could not understand the
role of the operators here.

Thanks,
Robert Scheer

[Randy Webb]

Re: Math.random syntax

Robert Scheer wrote:[color=blue]
> Hi.
>
> Reading about the Math.random method I saw that by default it
> generates between 0 and 1. To generate numbers between a greater range
> I can use these syntaxes:
>
> x = Math.random()/10[/color]

Divides the return from random() by 10, giving you a decimal form
between 0 and .1

[color=blue]
> x = Math.random()*1 0[/color]

Gives you a decimal integer between 0 and 10 by multiplying.
[color=blue]
> What is the difference between the two? I could not understand the
> role of the operators here.[/color]

One divides, one multiplies.

<URL: http://www.jibbering.com/faq/#FAQ4_22 />
might be a good resouce for you, the FAQ in its entirety but especially
that section.


--
Randy

[Lee]

Re: Math.random syntax

Randy Webb said:[color=blue]
>
>Robert Scheer wrote:[color=green]
>> Hi.
>>
>> Reading about the Math.random method I saw that by default it
>> generates between 0 and 1. To generate numbers between a greater range
>> I can use these syntaxes:
>>
>> x = Math.random()/10[/color]
>
>Divides the return from random() by 10, giving you a decimal form
>between 0 and .1
>
>[color=green]
>> x = Math.random()*1 0[/color]
>
>Gives you a decimal integer between 0 and 10 by multiplying.[/color]

No. It's not an integer.

The correct way to generate a "random" integer is described at:

http://www.jibbering.com/faq/#FAQ4_22

[Dr John Stockton]

Re: Math.random syntax

JRS: In article <bu6rvg010ed@dr n.newsguy.com>, seen in
news:comp.lang. javascript, Lee <REM0VElbspamtr ap@cox.net> posted at Thu,
15 Jan 2004 12:08:16 :-[color=blue]
>
>The correct way to generate a "random" integer is described at:
>http://www.jibbering.com/faq/#FAQ4_22
>[/color]

According to someone trustworthy, that method is not entirely reliable.
From a linked page :

Opera (5.02..6.01 at least), I have read, can give a value of 1.0
from its Math.random(), with a frequency of the order of one
in 35000 times - so that the function Random() below can
return N. There is a
<http://homepage.ntlwor ld.com/stephen.chalmer s/op6/random1.htm> Test
age by SC. Precautions are needed; appending %1 to Math.random()
should do. LRN 20030804 : Opera 4, 5, not 6.05.

Sometimes, returning N may not much matter; other times, it may cause
the page logic to fail, resulting in error but not necessarily obvious
error.

I do not know which values in 0..N-1 that 1/35000 probability is
extracted from (it is transferred to 0, of course, by %1). If a 1/35000
non-uniformity matters, ISTM that one should perhaps be using a better
algorithm and maybe another language.

function Random(N) {
do { T = Math.random() } while (T>=1.0) ; return Math.floor(N*T) }

may be better than

function Random(N) { return Math.floor(N*(M ath.random()%1) ) }


--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> jscr maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

[Harag]

Re: Math.random syntax

On 15 Jan 2004 06:11:26 -0800, rbscheer@my-deja.com (Robert Scheer)
wrote:
[color=blue]
>Hi.
>
>Reading about the Math.random method I saw that by default it
>generates between 0 and 1. To generate numbers between a greater range
>I can use these syntaxes:
>
>x = Math.random()/10
>x = Math.random()*1 0
>
>What is the difference between the two? I could not understand the
>role of the operators here.
>[/color]

At the moment I use the following function to get a randum "integer"
number, I'm new to Javascript so not sure if this is the best way...
its the way I did it in VBscript.

function RandomNumber (iMin, iMax) {
return Math.floor(((iM ax - iMin + 1) * Math.random()) + iMin);
}


HTH

Al.