How to correct index exceeds matrix dimensions error.

This is my codings. HEre it is showing error in the line data = symbols(x:x+3599); that is index exceeds matrix dimensions. Plz help me to clear this error.

clc;
clear all;
close all;
format long;
% GENERATION OF INFORMATION AND LDPC ENCODING
message= randint(1,43200); % INFORMATION BITS
H = dvbs2ldpc(2/3);
l = fec.ldpcenc(H);
codeword = encode(l,message);
figure;
    stem(codeword(1:100));
    xlabel('Samples');
    ylabel('Amplitude');
    title('LDPC encoding');
    inter = randintrlv(codeword,64800);
    figure;
    stem(inter(1:100));
    xlabel('Samples');
    ylabel('Amplitude');
    title('Interleaving');
   hMod = modem.qammod('M', 256);
 symbols = hMod.Constellation;
scatterplot(symbols);
% moutp = step(hMod, inter);
% mout = (moutp).';
symbols=symbols(:);
x = 1;
size(symbols);
for sym = 1:3  % SYMBOL LOOP
 data = symbols(x:x+3599);
   new_sym = zeros(1,3660);
    for i = 1:3600
        new_sym(i+30) = data(i);
    end
    p_sym = zeros(1,3780);
    d = sort(randint(1, 40, [2 3650])); % random index for central pilot
    for i = 1:39
        if (d(i+1) - d(i)) < 5
            d(i+1) = d(i+1) + 1;
        end
    end

Answer 1

[Walter Roberson]

The size of hMod.Constellation is going to be the same as the number you passed in for the 'M' parameter -- that is, 256. But you try to access up to element #3600 of it the first time you use it.