what does the "oldx =[x(n);oldx(1:256)]" in the following programm do?

fid = fopen('bbg1AR20.sig', 'r'); 
x = fread(fid,'int16')
oldx = zeros(256,1);
for n = 1: 256000
oldx =[x(n);oldx(1:255)];
end 

[ad lyn]

thnak you

what's about the 'r' here :fid = fopen('bbg1AR20.sig', 'r')

Answer 1

[David Hill]

for n = 1: 256000
  oldx =[x(n);oldx(1:255)];%just reforming the oldx array with x(n) on top and then the next 255 elements of oldx and dropping the last element
end 

Answer 2

[dpb]

It will (very inefficiently) append the first 255 elements of the (NEW and this is key) oldx vector onto the value of the read-in vector x after the Nth element, replacing the entire oldx vector on every pass through the loop. But, it is reversing x as it prepends it in front of the newly created vector each pass.

Whether this is the intent or not is probably debatable, but the above result is simply written as

oldx=[flipud(x);zeros(255,1)];

One might make presumptions of what was really intended, but that's what it does.