function value = trap_int ( a, b, fvec )
%
%  function value = trap_int ( a, b, fvec )
%
%  Return the value of the trapezoidal approximation to the
%  integral from A to B of F(X).  
%
%  FVEC is presumed to contain the value of F at equally
%  spaced points from A to B.
%
n = length ( fvec );

s = sum ( fvec ) - 0.5 * ( fvec(1) + fvec(n) )

value = ( b - a ) * s