# Logarithmic spiral

From JSXGraph Wiki

Revision as of 08:56, 25 June 2015 by A WASSERMANN (talk | contribs)

It can be described in polar coordinates [math](r, \theta)[/math] by the equation

- [math]r = ae^{b\theta}\,[/math]

with real numbers [math]a[/math] and [math]b[/math].

### The JavaScript code to produce this picture

```
board = JXG.JSXGraph.initBoard('jsxgbox', {boundingbox: [-10, 10, 10, -10]});
var a = board.create('slider', [[1,-1],[5,-1],[0,0.3,1]],{name:'a'});
var b = board.create('slider', [[1,-2],[5,-2],[0,0.15,1]],{name:'b'});
var c = board.create('curve', [function(phi){return a.Value()*JXG.Math.pow(Math.E,b.Value()*phi); }, [0, 0],0, 8*Math.PI],
{curveType:'polar', strokewidth:4});
var g = board.create('glider', [c]);
var t = board.create('tangent', [g], {dash:2,strokeColor:'#a612a9'});
```