Newton-Ralphson
method - or simply the Newton's method is one of the most commonly used
numerical searching method for solving equations. Usually
Newton's method converges well and quickly, but the convergence is not
guaranteed. Newton's method requires an initial value. This
values can determine the way the search is converged. The major
challenge to using this method is that the first differential (first
derivative) of the equation is required as an input for the search
precedure. Sometimes, it may be difficult or impossible to derive
that.
The example below demostrates the application using Newton-Ralphson
method to for solve 2 equations (both equations are set to zero)
individually. The first equation has one root (outcome) and the
second has two (see the charts). The method returns 0.56714 as
the value of the root for the first equation. We then plug this
value into the equation in cell D13 for checking and get a value of
zero - just as what we should be getting. It takes 4 steps (loops
or iterations) to converge.
Since equation 2 has two roots, we need to run the search precedure
twice - one for each of the first root and the second root. By
setting the initial value of 1 for first root search precedure, the
precudure converges after 5 steps and returns a velue of 1.79129.
The initial vlaue of the second root is set to -1 and the search
precedure converges after 7 steps with a returned value of
-2.79129. Both returned values are then plug into equation 2 for
checking and both checks return zero.
The first chart below shows the function line
intercepts the x-axis ( f(x)=0 ), at approximate 0.55. The
seconds chart shows the function line (curve) inptercepts the x-axis
twice, at around 1.8 and -2.8.
