Write MATLAB code to construct the matrices described below and visualise them using

imagesc. Do not use loops!

$($a$)$ The first matrix should have $16$ rows with consecutive integers from $1$ to N$,$ where N is

given by the user when prompted. The rows should be alternating: the numbers should be

in increasing order in row $1,$ decreasing order in row $2,$ increasing in row $3,$ decreasing in

row $4$ and so on$.$ An example for N $=20$ is shown in Figure $2\mathrm{.}6($a$).$

$($b$)$ The second matrix should be of size $10$ by $10.$ The exact colour of the blocks does not matter

as long as all $4$ colours are different and the colour of the central blocks are the same. An

example is shown in Figure $2\mathrm{.}6($b$).$

$($c$)$ The third matrix should appear as a colour frame of size M $($M rows and M columns$),$ where

M is given by the user, when prompted. An example for M $=10$ is shown in Figure $2\mathrm{.}6($c$)$