# Numerical Integration- Simpson’s Rule

If you’ve kept up on recent blog posts, you’ll notice that in our data one method for integration seemed to work without any error. This method was Simpson’s Rule. This fact sparked our interest as to why does this method work so well? In particular, we noticed that it was almost flawless with cubic functions. Why is this? From the text, we were given the idea to algebraically compute Simpson’s rule approximation and compare it to the actual integral of the special case in which our interval is [-h,h] and n, our number of rectangles, being 2 for $f(x)=ax^{3}+bx^{2}+cx+d$.

We began by computing the actual integration:

$\int\limits_{-h}^{h} (ax^{3}+bx^{2}+cx+d) dx$ $\implies$ ($\frac{ax^{4}}{4}$ + $\frac{bx^{3}}{3}$ + $\frac{cx^{2}}{2}$ + $dx$ + $C$)|$^{h}_{-h}$

[$\frac{ah^{4}}{4}$ + $\frac{bh^{3}}{3}$ + $\frac{ch^{2}}{2}$ + $dh$ + $C$]-[$\frac{a(-h)^{4}}{4}$ + $\frac{b(-h)^{3}}{3}$ + $\frac{c(-h)^{2}}{2}$ + $d(-h)$ + $C$]

$= \frac{2bh^{3}}{3} + 2dh$

The equation for Simpson’s Rule is $\frac{1}{3}[f(x_{i-1})+4f(x_{i})+f(x_{i+1})]h$

In using two rectangles we get: $\frac{h}{3}[f(-h)+4f(0)+f(h)]$ $\implies$ $\frac{h}{3}[(a(-h)^{3}+b(-h)^{2}+c(-h)+d)+4d+(a(h)^{3}+b(h)^{2}+c(h)+d)]$

$= \frac{h}{3}(2bh^{2}+6d)= \frac{2bh^{3}}{3} + 2dh$

And thus we find that in cubic functions Simpson’s rule is the most accurate method for computing the integration.

For further research we can look at what happens when we change the bounds to [a,b]. We can also calculate the actual integral and the Simpson’s rule for different types of functions too see if this method really holds up as being the most accurate method for numerical integration.

If you read my introduction, you probably already knew which lab I would pick. This lab is talking about Integration. It explains different way we can integrate, such as: Riemann Sum (Rectangle), Trapezoid Sum (Trapezoid, and Simpson’s Rule (parabola (dotted)). Integrations help us to calculate the approximate area underneath a given curve.
A question that will come up while working on this lab may be about comparing the few integration techniques listed previously. We will also be working with the difference of left hand, right hand and midpoint integration.
The reason I would like to work on this lab is because I have taken two and half calculus classes working with integrals and I would like to see if this opens my mind more to what exactly we are doing when we integrate.

# Samantha Intro For Funsies

I am Samantha (obviously). I am only three and a half semesters away from graduating with my Math Ed degree. Many of my current classes are not “new” to me. We are working on more of the teaching aspect. However, I am in Calc 3, that stuff is new. I love Calculus. I would rather not teach it, but I love working out the problems. Currently we are working with Integrals again. Integrals would be in my list of “Favorite Math Topics”. If you would like to know all about integrals, Wikipedia knows it!….: http://en.wikipedia.org/wiki/Integral
This is what they look like:
$\int_a^bf(x)dx$
In Calc three we are working with multi-variables, so they look like this:
$\int_a^b\int_c^dF(x)dxdy$

Fun, right?!