Lagrange polynomial

http://en.wikipedia.org/wiki/Lagrange_polynomial

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license : MIT License
modified : 2009-07-01 15:16:39

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// http://en.wikipedia.org/wiki/Lagrange_polynomial
package {
    import flash.display.Sprite;

[SWF(frameRate="7")] 
    public class FlashTest extends Sprite {
        public function FlashTest() {
            Wonderfl.capture_delay (10);
            stage.addEventListener ("mouseDown", onMouseDown);
            stage.addEventListener ("mouseUp", onMouseUp);
            stage.addEventListener ("enterFrame", onEnterFrame);
        }

public var mouseDown:Boolean = false;
        public function onMouseDown (e:*):void {
            posx.length = 0;
            posy.length = 0;
            mouseDown = true;
        }
        public function onMouseUp (e:*):void {
            mouseDown = false;
        }

public var posx:Array = [];
        public var posy:Array = [];
        public function onEnterFrame (e:*):void {
            if (mouseDown) {
                posx.push (mouseX);
                posy.push (mouseY);
            }

var i:int = 0, ts:Array = [];
            graphics.clear ();
            graphics.lineStyle ();
            graphics.beginFill (0xFF0000);
            for (i = 0; i < posx.length; i++) {
                ts.push (i);
                graphics.drawCircle (posx [i], posy [i], 3);
            }

graphics.endFill ();
            if (!mouseDown && (posx.length > 1)) {
                graphics.lineStyle (0, 0);
                for (var t:Number = 0; t < 100; t += 0.1) {
                    var tx:Number = lagrangeInterpolatingPolynomial (
                        ts, posx, t);
                    var ty:Number = lagrangeInterpolatingPolynomial (
                        ts, posy, t);
                    if (t == 0)
                        graphics.moveTo (tx, ty);
                    else
                        graphics.lineTo (tx, ty);
                }
            }
        }

public function lagrangeInterpolatingPolynomial (
            pos:Array, val:Array, desiredPos:Number):Number {
            var degree:int = pos.length;
            var retVal:Number = 0;

for (var i:int = 0; i < degree; i++) {
                var weight:Number = 1;

for (var j:int = 0; j < degree; j++) {
                    // The i-th term has to be skipped
                    if (j != i) {
                        weight *= (desiredPos - pos[j]) / (pos[i] - pos[j]);
                    }
                }

retVal += weight * val[i];
            }
 
            return retVal; 
        }
    }
}

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