AEF.NEC Numerical Estimation Comparison ("The More, The Merrier")
In this subsection we compare the three previously discussed techniques
for making numerical estimates for solutions to an equation using
mapping diagrams to visualize these techniques. Each method starts with
the assumption that $f$ is a continuous function on the interval
$[a,b]$ and $0$ is between $f(a)$ and $f(b)$, which allows the use of
the following theorem to guarantee a solution to the equation $f(x)=0$, i.e., a number $c \in [a,b] $ where $f(c) = 0$
Theorem: CCD.IVT.0: If $f$ is a continuous function on the interval
$[a,b]$ and $0$ is between $f(a)$ and $f(b)$, then there is a number $c \in [a,b]$
where $f(c) = 0$.
There are three main issues with numerical methods once there is a guarantee that there is a number to be estimated:
- Is the method easy to follow? Is the method pactical? Of the three
methods, only the Newton secant method can be impractical because it
has the potential to fail by enountering a loop where values for
estimated repeat or there is a possibility that $f(a_n) = f(b_n) \ne 0$.
- Will the method assure better estimates for the desired solution?
Is the method effective? Again- Of the three methods, only the Newton
secant method can be ineffective
because it has the potential to fail by enountering a loop where values
for estimated repeat or there is a possibility that $f(a_n) = f(b_n) \ne
0$ or fall outside the inital interval where a solution is guaranteed.
- How quickly will the method arrive at a desired level of accuracy?
Is the method efficient? Despite the risks, in practice the Newton
secant method is often the most efficient, with false position also
better than the slow but steady bisection method
Comparison of Methods
This example allows you to change the method being applied at any stage
for comparison of the effectiveness and efficiency of each method:
To change the method being applied, move the position of the slider labeled "Method."
- false position, or
- Newton secant.
Notice how the arrows on the mapping diagram are paired with the
point on the graph of the function $f$.
You can move the point for $x$ on the mapping diagram to see how
the function value changes both on the diagram and on the graph.
Sliders: The sliders labeled $a$ and $b$ control the end values of the initial interval $[a,b]$.
The slider labeled $n$ controls which the number of times the Newton secant method is executed.
Checking the box to "Show/Hide Secant Point Position & Data" will
display $a_n, b_n, P_n$ and the values of $f$ for each of these
It will also display a second box to "Show/Hide Smallest Exact
Root". Checking this box will display this root on both the graph and
the mapping Diagram.
The function $f$ can be changed by making an entry in the appropriately labeled input box.
Martin Flashman, August. 10, 2017.
Created with GeoGebra