1. Error Formula

For the recursive algorithm p0=1, p1=1/3, pn=(10/3)(pn-1 - pn-2) for n >1 let the error be denoted by p'=pn+en for initial error e0, and assume the error has the form

p'0=p0+e0
p'1=p1+3e0
p'n=(10/3)(p'n-1 - p'n-2) for n>1

so that e1=3e0
Find an equation for en in terms of e0, n, and a constant.

2. Re: Error Formula

Originally Posted by veronicak5678
For the recursive algorithm p0=1, p1=1/3, pn=(10/3)(pn-1 - pn-2) for n >1 let the error be denoted by p'=pn+en for initial error e0, and assume the error has the form

p'0=p0+e0
p'1=p1+3e0
p'n=(10/3)(p'n-1 - p'n-2) for n>1

so that e1=3e0
Find an equation for en in terms of e0, n, and a constant.
$p'_n=(10/3)[p'_{n-1}-p'_{n-2}]$

is a linear difference equation, so suppose $p'_n=A^n$ for some real number $A$, then find the characteristic equation and solve for $A$. Form the general solution as a linear combination of the two solutions you will have found and fit to the initial conditions.

CB

3. Re: Error Formula

Could you please explain how to find the characteristic equation?

4. Re: Error Formula

Originally Posted by veronicak5678
Could you please explain how to find the characteristic equation?
You make the substitution $p'_n=A^n$ in the difference equarion to get:

$A^n=\frac{10}{3}[A^{n-1}-A^{n-2}}]$

Now divide through by $A^{n-2}$ to get:

$A^2=\frac{10}{3}[A-1]$

which is a quadratic in $A$ which rearranges to:

$A^2-(10/3)A+(10/3)=0$

which is the charateristic equation which you solve for $A$.

CB

5. Re: Error Formula

I see. Thanks!