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
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