$1.[8$ points.$]$ Logical Subscripting. Write a separate m$-$file for each part.

$($a$)$ Use logical subscripting to compute and plot the following piecewise defined function

f$($x$)$ of one variable on the interval $[0,4]$:

$2$x if x $<=12,$ f$($x$)=2($x$1)$if$211.$