how to calculate the difference between current and previous value if the values are first element of single column ?

I am writing a program which has loop, for each loop the output is single column of size Mx1, I want to apply DPCM for the first element of each column in the loop and store it to its position.

how to write matlab code for DPCM?

thank you in advance

[per isakson]

See https://se.mathworks.com/help/comm/ug/differential-pulse-code-modulation.html