code: protected double trapezoid( int n ) {
          double x = 0;
          double tnm = 0;
          double sum = 0;
          double del = 0;
          int it = 0;
          int j = 0;
  
          if (n == 1) {
              strapezoid = 0.5f * (upperlimit - lowerlimit)
                      * (equation(lowerlimit) + equation(upperlimit));
          } else {
              /*
               * for (it = 1, j = 1; j < n - 1; j++) { it <<= 1; }
               */
              it = (int) Math.pow(2.0, n - 1);
  
              tnm = (double) it;
              del = (upperlimit - lowerlimit) / tnm;
              x = lowerlimit + 0.5f * del;
              for( sum = 0f, j = 1; j <= it; j++, x += del ) {
                  if (x >= upperlimit) {
                      System.out.println("hoi");
                  }
                  sum += equation(x);
              }
              strapezoid = (double) (0.5f * (strapezoid + (upperlimit - lowerlimit) * sum / tnm));
          }
  
          return strapezoid;
      }
docs: Calculate the integral with the trapezoidal algorithm of the equation implemented in the
  method equation
  
  @param n - number of steps to perform
  @return