Untitled

how to generate amplitude modulated sine wave in iphone sdk?
float x=75;
float yc=50;
float w=0;
 while (w<=rect.frame.size.width) {
CGPathMoveToPoint(path, nil, w,y/2);
CGPathAddQuadCurveToPoint(path, nil, w+x/4, -yc,w+ x/2, y/2);
CGPathMoveToPoint(path, nil, w+x/2,y/2);
CGPathAddQuadCurveToPoint(path, nil, w+3*x/4, y+yc, w+x, y/2);
CGContextAddPath(context, path);
CGContextDrawPath(context, kCGPathStroke);
w+=x;
}