function t = adaptrap(f,a,b,n)
%
%  function t = adaptrap(f,a,b,n)
%
%  Returns a vector of n approximations for the definite integral of
%  the function f over the interval [a,b], the i-th entry in the vector
%  uses 2^i function evaluations.
%
%  Example:
%    t = adaptrap('sin',0,pi/2,10);
%
t = zeros(n,1);
h = (b-a);        % size of subinterval
m = 1;            % number of subintervals
t(1) = (feval(f,a) + feval(f,b))*h/2;
for i = 2:n
   h = h/2;
   for j=0:m-1
      t(i) = t(i) + feval(f,a+h+j*2*h);
   end;
   t(i) = t(i-1)/2 + h*t(i);
   m = 2*m;
end;