Index exceeds matrix dimensions.

check_data=test_data_in(1:600);
for i=1:600
    check_data(i)=test_data_in(randi(numel(test_data_in)))
end 

[Jan]

You forgot to ask a qeustion.

Answer 1

[Jan]

Your code runs without problems:

test_data_in = rand(1, 1000);
check_data = test_data_in(1:600);
for i = 1:600
    check_data(i)=test_data_in(randi(numel(test_data_in)));
end 

So what is your problem?

Does your test_data_in has less than 600 elements?