JavaScript Math vs Excel

[Lenni]

Hi,

I'm currently writing a web application for bicycle wheel builders
that calculate the spoke length for all sorts of variations of hubs
and rims.

I have translated the formula from an Excel spreadsheet and in
JavaScript it looks like this:

var sll=Math.sqrt(M ath.pow(((fdl/2*Math.sin((2*M ath.PI*cross)))/
(spokes/2)),2)+Math.pow ((erd/2-((fdl/2)*Math.cos(2*M ath.PI*cross/
(spokes/2)))),2)+Math.p ow((c2l+osb),2)-shd/2);

The problem is that I get slightly different results when I use
JavaScript than when I use Open Office Calc. It isn't much, less than
a millimeter, which shouldn't really matter when you're building a
wheel but it is slightly worrying me.

My question, is it possible that the JavaScript Math object is not as
powerful as the Excel or OpenOffice one and that there are just slight
rounding errors that are causing this disparity? Or to rephrase the
question, can I stop checking the formula over and over again for
errors?

Thanks
Lenni

[gimme_this_gimme_that]

Speaking of VBScript - the strategy you should take is to write the
Function in Excel VBA - then translate to VBScript.

You started with Excel formulas - you need to start with Excel VBA.

[sasuke]

On Oct 28, 2:03*pm, "Evertjan." <exjxw.hannivo. [e-mail] wrote:

SAM wrote on 27 okt 2008 in comp.lang.javas cript:

avascript calculate on base 64 (I think, or something like that) and
sometimes it can't give the exactly number such as :
1.0000000009
instead of 1

You could try by using your variables multiplied by 1000 or 100000
and finally get back the roundness of the result divided by the same
coefficient

Such division could sometimes introduce the same kind of error, methinks.

Better use regex do a string manipulation imitating such division:

var aNumber = 1.2345
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)$/,'.$1')

var aNumber = 1.2345678;
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)$/,'.
$1');
alert(resultStr ing); // 1235.0.678

../sasuke

[Evertjan.]

sasuke wrote on 30 okt 2008 in comp.lang.javas cript:

>Better use regex do a string manipulation imitating such division:

var aNumber = 1.2345
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)$/,'.$

1')

var aNumber = 1.2345678;
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)$/,'.
$1');
alert(resultStr ing); // 1235.0.678

You are right, should be[, only where the absolute value is above 1]:

var aNumber = 1.2345678;
var resultString =
Math.floor(aNum ber*1000+.5).to String().replac e(/(\d\d\d)$/,'.$1');
alert(resultStr ing); // 1.235


--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Evertjan.]

Evertjan. wrote on 30 okt 2008 in comp.lang.javas cript:

sasuke wrote on 30 okt 2008 in comp.lang.javas cript:

>>Better use regex do a string manipulation imitating such division:

var aNumber = 1.2345
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)

$/,'.$

>1')

var aNumber = 1.2345678;
var resultString = (aNumber*1000+. 5).toString().r eplace(/(\d\d\d)$/,'.
$1');
alert(resultSt ring); // 1235.0.678

You are right, should be[, only where the absolute value is above 1]:

var aNumber = 1.2345678;
var resultString =
Math.floor(aNum ber*1000+.5).to String().replac e(/(\d\d\d)$/,'.$1');
alert(resultStr ing); // 1.235

Wow, not that easy in regex, try:

<script type='text/javascript'>

function round3dec(x) {
x = Math.floor(x*10 00+.5)+'';
var s = x.replace(/(^\-?).*/,'$1');
x = x.replace(/^\-?/,'0000');
return s + (1*x.replace(/\d\d\d$/,'')) + '.' +
x.replace(/-?\d*(\d\d\d)$/,'$1');
};

alert( round3dec(21.23 45678) );
alert( round3dec(-21.2345678) );
alert( round3dec(0.002 5555) );
alert( round3dec(-0.0025555) );

</script>
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Conrad Lender]

On 2008-10-30 21:59, Evertjan. wrote:

Wow, not that easy in regex, try:

<script type='text/javascript'>

function round3dec(x) {
x = Math.floor(x*10 00+.5)+'';
var s = x.replace(/(^\-?).*/,'$1');
x = x.replace(/^\-?/,'0000');
return s + (1*x.replace(/\d\d\d$/,'')) + '.' +
x.replace(/-?\d*(\d\d\d)$/,'$1');
};

alert( round3dec(21.23 45678) );
alert( round3dec(-21.2345678) );
alert( round3dec(0.002 5555) );
alert( round3dec(-0.0025555) );

</script>

(10000000000000 00000).toFixed( 3)
-100000000000000 0000.000

round3dec(10000 00000000000000)
-1e+21.00001e+21

:-)
- Conrad

[sasuke]

On Oct 31, 2:57*am, Conrad Lender <crlen...@yahoo .comwrote:

On 2008-10-30 21:59, Evertjan. wrote:

Wow, not that easy in regex, try:

<script type='text/javascript'>

function round3dec(x) {
* x = Math.floor(x*10 00+.5)+'';
* var s = x.replace(/(^\-?).*/,'$1');
* x = x.replace(/^\-?/,'0000');
* return s + (1*x.replace(/\d\d\d$/,'')) + '.' +
* * x.replace(/-?\d*(\d\d\d)$/,'$1');
};

alert( round3dec(21.23 45678) );
alert( round3dec(-21.2345678) );
alert( round3dec(0.002 5555) );
alert( round3dec(-0.0025555) );

</script>

(10000000000000 00000).toFixed( 3)
* -100000000000000 0000.000

round3dec(10000 00000000000000)
* -1e+21.00001e+21

:-)

LOL, that's a nice one. Moral of the story: Use built-in functions
whenever possible. ;-)

../sasuke

[Evertjan.]

sasuke wrote on 31 okt 2008 in comp.lang.javas cript:

On Oct 31, 2:57*am, Conrad Lender <crlen...@yahoo .comwrote:

>On 2008-10-30 21:59, Evertjan. wrote:

Wow, not that easy in regex, try:

<script type='text/javascript'>

function round3dec(x) {
* x = Math.floor(x*10 00+.5)+'';
* var s = x.replace(/(^\-?).*/,'$1');
* x = x.replace(/^\-?/,'0000');
* return s + (1*x.replace(/\d\d\d$/,'')) + '.' +
* * x.replace(/-?\d*(\d\d\d)$/,'$1');
};

alert( round3dec(21.23 45678) );
alert( round3dec(-21.2345678) );
alert( round3dec(0.002 5555) );
alert( round3dec(-0.0025555) );

</script>

(1000000000000 000000).toFixed (3)
* -100000000000000 0000.000

round3dec(1000 000000000000000 )
* -1e+21.00001e+21

:-)

LOL, that's a nice one. Moral of the story: Use built-in functions
whenever possible. ;-)

Not at all, there is no joy in using build-in functions,
but for those who love production.

The above example of conrad is out of bounds in normal use.

Regex is a joyful puzzle by itself.
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Dr J R Stockton]

In comp.lang.javas cript message <ca9917a8-230f-48df-a016-1efe5081a3fa@i1
8g2000prf.googl egroups.com>, Fri, 31 Oct 2008 07:15:36, sasuke
<da*********@gm ail.composted:

>
LOL, that's a nice one. Moral of the story: Use built-in functions
whenever possible. ;-)

But only where they are trustworthy on "all" systems. Method toFixed
has errors in IE.

--
(c) John Stockton, near London. *@merlyn.demon. co.uk/?.**********@ph ysics.org
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