Hi, Before answering the question, I want to give you a couple of suggestions.
First, try to post your code in better format. It is really hard to read (put the code in "code" style, and try to use one instruction per row).
Second, if you try your code one instruction at a time, it's much easier to find where the error is located. Or, even better, put your code in a script/function file and then try to execute it. Matlab will give you details about where the error is found. (Error in eren_baris (line 7) k=N_a(w/3e8);)
Let's answer your question now. You wrote
but probably, you wanted
Without the multiplication, matlab is interpreting w/3e8 as an index for N_a. But w/3e8 is not an integer, and thus can't be an index. Moreover, in this case, N_a is not even a vector.