>> [t,x,y] = sys_runge_kutta_2(-2,1,0,3,.001);
>> plot(x,y,'--')
>> hold on
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(2,-1,0,3,.001);
>> plot(x(1),y(1),'o')
>> plot(x,y,'--')
>> [t,x,y] = sys_runge_kutta_2(.2,.1,0,3,.001);
>> plot(x,y,'--')
>> plot(x(1),y(1),'o')

% the third curve shot off to huge values, so I reset the axis so that
% I can see what's going on. 

>> axis([-3,3,-3,3])
>> [t,x,y] = sys_runge_kutta_2(-.2,-.1,0,3,.001);
>> plot(x(1),y(1),'o')
>> plot(x,y,'--')
>> [t,x,y] = sys_runge_kutta_2(-2,1.1,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(-2,.9,0,3,.001);
>> plot(x(1),y(1),'o')
>> plot(x,y,'-')
>> [t,x,y] = sys_runge_kutta_2(-2,.95,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(-2,1.05,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(2,-1.05,0,3,.001);
>> plot(x(1),y(1),'o')
>> plot(x,y,'-')
>> [t,x,y] = sys_runge_kutta_2(2,-1.1,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(2,-.9,0,3,.001);
>> plot(x(1),y(1),'o')
>> plot(x,y,'-')
>> [t,x,y] = sys_runge_kutta_2(2,-.95,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')
>> [t,x,y] = sys_runge_kutta_2(2,-1.5,0,3,.001);
>> plot(x,y,'-')
>> plot(x(1),y(1),'o')

% okay, I've decided I made a mistake and I don't want that last curve
% on the plot.  So I plot over it with white (if the background of the
% plot is white).  This just means saying 'w-' and 'wo' for "white
% solid line and white open circle.  If the background of the plot is
% black then it's 'k-' and 'ko'.

>> plot(x,y,'w-')
>> plot(x(1),y(1),'wo')
>> axis([-2.5,2.5,-2.5,2.5])
>> print -dps fig.ps
>> title('this is a title')
>> xlabel('x axis')
>> ylabel('y axis')
>> gtext('write something here')

% note, gtext requires you to position the words "write something
% here" to the desired position and then click the mouse to stick them
% there.

>> quit



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