| Trapezoids provide an improved match to the shape 
              of curving function as compared to rectangles but they are still 
              are linear. A polynomial curve for the top of the slice should provide 
              a better match to many functions and allow for fewer slices over 
              which to sum, thereby speeding computation and reducing roundoff 
              errors. If we use the second order Lagrange interpolation 
              formula with a fixed slice width  :     and integrate from xi 
              to xi+2 the 
              area is      which is the area beneath a parabola. Summing these over all the slices leads to            This is called Simpson's rule. Note that it 
              requires an even number of slices. References & Web Resources |