function slideshow(x,y,f,step,fix,hld,ttl,xlab,ylab,tlab,nmin,nmax,col,f2,col2);
 
  $Id: slideshow.m,v 1.18 2003-01-27 10:22:44-06 brinkman Exp $
  (c) 2001, Peter Brinkmann (brinkman@math.uiuc.edu)
 
  slideshow: shows successive slices of a grid of values
 
  Usage: slideshow(0:0.1:1,0:0.1:1,f,1,1,0,'title','x','y','g');
 
  Parameters:
 	x: row vector of x-values
 	y: row vector of y-values
 	f: grid of values f(x,y)
 
  Optional parameters:
 	step: nonzero value means step-by-step, 0 means animation (default 1)
 	fix: nonzero value indicates fixed axes (default 1)
 	hld: nonzero value indicates that successive plots are superimposed
 			(default 0)
 	ttl: title string (default 'no title')
 	xlab: label of x-axis (default ' ')
 	ylab: label of y-axis (default ' ')
 	tlab: label of t-axis (default ' ')
 		This is the time axis of the slide show.
 	nmin: index of initial slide (default 1)
 	nmax: index of terminal slide (default length(y))
 	col: color of plot (default 'r')
 	f2: row vector of values f(x) to be plotted on every slide (default [])
 	col2: color of plot of f2 (default 'b')