Digital Signal Processing - Downsampling Assignment

The operation of signal Dilation(Decimation/Downsampling) is defined by;

y[n] = x[nM]

in which x[n] is downsampled by a factor of M.

for example;

               If x[n] = {..., -2, 4, 3, -6, 5, -1, 8} 

then downsampled sequence by a Factor of 2 is given by; 

y[n] = {... ... ...}.

1. Develop a MATLAB function named "dnsample" that has a form;

"function = dnsample(n, M)"

     2.   Generate;

x[n] = sin(0.125πn)              where -50 ≤ n ≤ 50

Decimate(Downsample) x[n] by a factor of 4 to generate y[n]. Plot both x[n] and y[n] and comment on the result. Repeat the above using 

x[n] = sin(0.5πn)                   where -50 ≤ n ≤ 50

Discuss the effect of the sampling on the signal.

* If you know the code please text me.