function int = trap1(f, a, b)
    % Input - f is the integrand input as a string 'f'
    % - a and b are upper and lower limits of integration
    % Output - int is the trapezoidal rule sum
    if a > b
        error('b must be greater than a');
    end
    h = (b - a);
    int = h * (feval(f, a) + feval(f, b)) / 2;
end