%
%  code1Fa.m -- 06 sept 02 -- djm
%
%  - to run, type "code1Fa" at the matlab prompt ">>"

%  clear workspace & graphics

clear;  close all

%  set t & v grid matrices ("help meshgrid")

t = 0:1:10;  v = 40:1:60;
[tt,vv] = meshgrid(t,v);

%  calculate tangent vectors (dt,dv)

dt = ones(size(tt));  dv = 9.8 - vv/5;

%  plot tangent vectors ("help quiver") 

figure(1);  hold on
quiver(tt,vv, dt, dv,0.5,'k')
quiver(tt,vv,-dt,-dv,0.5,'k.')
plot(tt(:),vv(:),'r.')
axis([-0.5 10.5 39 61]);

%  label plot

title(['tangent vectors (figure 1.1.2)'])
xlabel('t-axis')
ylabel('v-axis')

disp('hit return to continue')
pause

%  plot ODE solution through (2,44)

t1 = -1:0.1:11;  
v1 = 49 - 5*exp((2-t)/5);
plot(t,v1,'g')