Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cmcl2!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: Mandlebrot set
Keywords: fractal, mandelbrot, julia, graphics
Message-ID: <10479@smoke.BRL.MIL>
Date: 2 Jul 89 03:09:26 GMT
References: <2492@blake.acs.washington.edu> <225800193@uxe.cso.uiuc.edu> <1354@uceng.UC.EDU>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 36

In article <1354@uceng.UC.EDU> mfinegan@uceng.UC.EDU (michael k finegan) writes:
>    While the calculation of members of the Mandelbrot set may be well known, do
>you have pseudo-code for calculation of members of a Julia set?

There are all sorts of clever schemes, but the following extract from a
program that creates Mandelbrot & Julia convergence displays in the
"obvious" way shows that the calculations are quite similar:

	if ( julia )
		{
		zx = cx;
		zy = cy;
		for ( k = 0; k < iters; ++k )
			{
			register double	x = zx * zx - zy * zy + jx;

			zy = 2.0 * zx * zy + jy;
			zx = x;

			if ( zx * zx + zy * zy >= thresh )
				break;
			}
		}
	else	{	/* mandelbrot */
		zx = zy = 0.0;
		for ( k = 0; k < iters; ++k )
			{
			register double	x = zx * zx - zy * zy + cx;

			zy = 2.0 * zx * zy + cy;
			zx = x;

			if ( zx * zx + zy * zy >= thresh )
				break;
			}
		}