updating 'content' of css style from a java script function?

[notageek]

I want to have a java script function to change the 'width' to 100px, as in the example below. I already know how to do it by calling a separate style class:

document.getElementById('dynamicPicture').className="size1";

but would like to add some "mathematics" to dynamically set 'width'.
What is the syntax?
Thank you.

img.size0 {
width:50px;
}

Thanks.

[Fang]

1. In IE and Opera (partially I believe), you can use dynamic properties - not supported in Moz. browsers

2. DOM access to style sheets. Unfortunately you can only access the index of the rule and not the class selector name.

3. Find the relevant elements by searching the DOM tree:

var aIMG=document.getElementsByTagName('img');
for(var i=0; i<aIMG; i++) {
    if(aIMG[i].className=='size0') {
        aIMG[i].style.width=aValue+'px';
        }
    }

[notageek]

Thanks.
I was also recommended:
document.getElementById('dynamicPicture').style.width=w+'px'
(which is similar to your sugestion), and it works fine in my case.