$2.$ Write a function in M file to generate a cosine wave with the following specifications:

$$ Name the function as cosgen

$$ f $=$ desired frequency

$$ dur $=$ duration of the waveform in seconds

$$ take $20$ samples per period

$$ plot the cosine function

Write the function in M$-$file and execute the program in MATLAB command window. Prove that your program works for $2000$Hz and $3000$ Hz$.$ Plot the function for $3$ cycles.