
	X P L O T,  Version Beta  Feb.  9, 1995
	Maorong Zou, Dept. of Math. UT Austin
help:
	Usage: help topic. Available topics are:

	surface,   curve,   tube,   datafile,   object,   
	function,   variable,   dummy_variable,   operator,   plot,   
	show,   quit,   title,   save,   load,   
	

surface:
	 A surface is either the graph of a 2 variable function f(x,y) or a
	 parametric surface or a polygon list described by the OFF format.
	 For example,
 	  a = surface{[ exp( -(x^2+y^2)) ][x= -1:1][y=-1:1]};
	  b = surface{[ cos(x)*cos(y),cos(x)*sin(y),sin(x)][x=-0.5*pi,0.5*pi]
		 [y=0:2*pi] [sample=30:40]};
	  c = surface{["sample_data_file"]};


curve:
	 A space curve can be defined by a data_file or by its parametric 
	 coordinate functions. 
 	   For example,
	    d = curve{["sample_datafile"][style=points]};
	    e = curve{[sin(x),cos(x),0][x=0:2*pi][sample=200][color=red]};
	 There are two styles for curves. Solid (default) and points.

tube:
	 Tube defines a tube around a space curve, 
	   For example,
	    torus =tube{[cos(x),sin(x),0][x=0:2*pi][radius=0.3][sample=80:20]};
	    torus1=tube{[cos(x),sin(x),0][x=0:2*pi][radius=0.15+0.1*sin(x)]};
	    f = tube{["sample_datafile"][radius=0.2]};

datafile:
	 Xplot accepts the following types of datafiles.
		 M by N GRID 
	 where the datafile contains of MN lines, each line consists of
	 three floats (the x,y,z coordinates of a point). This type of data
	 can be used to define a surface, for example
		 g = surf{["grid_data"][sample=32:32]};
	 A M by 1 grid can be used to define a curve or a tube, for example,
		 h=curve{["A_M_by_1_grid"]}; i=tube{["M_by_1_data"][radius=1]}
		 Polygon list (OFF format)
	 This type of data can be used to define a surface. 

object:
	 An object is a group of simple graphs, for example
		  a = sur{[x*y][x=-1:1][y=-1:1]};
		  b = cur{[x,x^2,x^3][x=-1:1]};
		  o=object{ a, b}

function:
	 You can define your own functions via some of the standard math
	 functions and operators. For example
		 f(x) = exp( sin(x) +0.2);
		 g(x,y) = tan(x) + log( abs(x)) *sqrt( x^2+1);
		 r(x)=(x<=0.0? -4*x + 0.1 : (x<=2.0? 0.1: sqrt((1.3*(x-2)))))
	 Here is a list of bulid in functions

		  sin   cos     tan   
		  sinh  cosh    tanh  
		  asin  acos    atan 
		  abs   sqrt    pow   
		  log   log10   exp   
		  real imag conjg arg  
		  besj0  besj1  besy0 besy1  
		  floor  ceil   int  
		  rand   

variable:
	 Variable are just numbers, for example,
		 sqrt3 = sqrt(3);
		 lambda = real( exp( 3 + 2* i));
	 There are two internal variables, pi = 3.1415926,  i= sqrt(-1);

dummy_variable:
	 Dummy variables are names of function arguments. The defaults are
		  x, y, z, w
	 You can overwrite the defaults by the 'set dummy' command. For example
		 set dummy u,v;
	 will set the dummy variables to  u,v,z,w. To see what are the current
	 dummy variables, use the 'show dummy' command.

operator:
	 Here is a list of math operators,
		    +    -    *    /    %       (basic arithmetic) 
		    ^    **                     (exponentiation) 
		    &&   ||   !                 (logical) 
		    ==   <=   >=  >   <   !=    (relational) 
	 These operators can be used in defining variables and functions.

plot:
	 To plot a defined object, use 'plot obj_name'. For example
		  a = sur{[sin(x)*cos(y)]};
		  plot a;

show:
	 The 'show' command displays you the defined objects. for example,
		 show func
	 displays all the defined functions and the command 
		 show all
	 displays all the defined objects (functions, variables, graphical objs)

quit:
	 The 'quit' command terminates Xplot. If followed by a string (meanining	 text in double quotes), it save all your command to the file with name
	 the string. For example,
		 quit "session1"
	 will save all your command to 'session1'


title:
	 The 'set title' command allows you to set the plot title. For example
		  set title "This is a sample plot"
	 produces a plot title "This is a sample plot".
	 Once a plot is done, you can move the position of the text by picking
	 the text with the left mouse button and move the pointer around. The 
	 color of the title may be modified by pressing the middle mouse button 
	 on the text. You can also change the font by pressing the right button
	 on the text.

	 To disable the plot title, use the command 'set notitle'

	 To see the current plot title, use the command 'show title'

save:
	 The 'save' command save selected commands to a file. For example,
		 save all "xplot.com"
	 save all commands entered to the file "xplot.com"
	 File saved by xplot can be loaded later via the `load` command.

load:
	 The 'load' command reads and executes the commands from a file.
	 For example,
		 load "xplot.com"
	 executes all commands in "xplot.com"

