Write a function that calculates permutations. Permutations help us figure how many unique possibilities exist when you take for example a $4$ digit pin code based on digits from $0-9.$ In permutations, the order does matter. $($this is the opposite of combinations$).$

We typically define this be describing it as $\backslash ($ n $\backslash )$ objects taken $\backslash ($ r $\backslash )$ at a time. In the above example, our n objects are the digits Zero through Nine... so $\backslash (\backslash$mathrm$\{$n$\}=10\backslash ).$ And since we have $4$ digits in the pin code, $\backslash ($ r$=4\backslash ).$

The formula to calculate the permutations is given as:

$\backslash [$

P$($n$,$ r$)=\backslash$frac$\{$n$!\}\{($n$-$r$)!\}$

$\backslash ]$

Write a function that takes the input parameters and computes the permutations. Please execute this script without using MATLAB's built$-$in factorial. In other words, you will most likely need to use for loop$($s$)$ for this calculation. $($Hint$,$ you could check your code by using MATLAB's built$-$in for factorial pun intended$)$

Be sure to develop a structure plan or psuedo code that you write before actually writing the commands.