For the Derivation of formula a tool is used, as is often the case in mathematics. The original function from the original area (time area) is first transformed into the image area, where it is processed with simple tools and then transformed back into the original area. For example, the Laplace transform is a very suitable tool for solving differential equations.
With it a time function f(t) will assigned with the so-called one-sided Laplace transformation by means of the Laplace
a complex function of frequency..
The Laplace transform of derivatives can be determined as follows:
Important is the time shifting function to right.
Using Laplace transform a differentiation in the original area shall be a multiplication in the image area.
For the reverse transformation back to the original area can be used the so-called Residue formula
Here, n is the order of the pole at p=pν.
Is f(t) not a continous function but a sequence [xn], then can be used the discrete Laplace-Transformation (L
If in this formula will set e
This results in the following transformation and revers transformation rules:
In this case is p the order of the pole at z=zk.
Again, the time shifting is importent for the solution of our problem.
Such as the Laplace transform is suitable for solving differential equations, the z-transform can be used to solve difference
Calculation using z-transformation
As already shown, is the rule for the Fibonacci numbers
with the initial conditions
To use the the right side time shift, which considered the initial conditions, the formula is slightly redesigned, and it is used the variable x .
So, it follows
The application of the z-transformation yields
From the last equation follows
Now the inverse transformation can be done using the Residue formula.
Because z1 and z2 are simple poles, is for both cases p=1.