algorithm - Trapez Method in Java -

I found a formula in calculating Trapejhoid method, it works as it should, but I do not know Why should I have the following lines in the Trape method :

  yoga = 0.5 * bf + (h * yoga);  First :  
  tra [0] = 0.5 * done by the following command in I = i + 2  
 
 ((B - A) / N) * (function (A) + function (B)); // Calculates the first step value of  

Trape method for the next iteration:

  / ** * Next calculation step with Tripjh method * @param e-Louvre border * @param B. On the border * @ Param beef-Preepr step value * @param N -nmber of Divijning Rating * Return Integral area * / public static double Fajhej (Double a , Double b, double beef, int n) {double sum = 0; Double H = ((B - A) / N); For (int i = 1; i  

function will be accompanied by a driver loop doubles the number of which The refinement is less than the threshold criterion, refining the approximate integral to the subdivision on each iteration, from a repetition to the difference.

By considering the function value, consider what is required when applying the Trepidoid rule on given. Now, consider the values ​​of the functions required to divide each subinterval into half and apply trapezoid rules to those sub-channels. In the latter case, half of the required function values ​​(give or take 1) are already the same as needed. The values ​​already computed in the code presented are duplicated ( 0.5 * bef ), they only add new values ​​( i = i + 2 ).

Note that for the code to be correct, it seems that the argument should be n