error shows up when run the code

% Clear all variables and close all figures
clear all; clf;

% Set the mode to 1 for regularized channel inversion
mode = 1;

% Set the number of frames per packet and the number of packets
N_frame = 10;
N_packet = 200;

% Set the number of bits per frame and the total number of bits
b = 2;
NT = 4;
N_user = 20;
N_act_user = 4;
I = eye(N_act_user, NT);
N_pbits = N_frame * NT * b;
N_tbits = N_pbits * N_packet;

% Set the range of SNR values
SNRdBs = (0:2:20);
sq2 = sqrt(2);

% Initialize the BER vector
BER = zeros(length(SNRdBs), 1);

% Loop over the SNR values
for i_SNR = 1:length(SNRdBs)
    
    % Set the SNR
    SNRdB = SNRdBs(i_SNR);
    
    % Initialize the number of errors
    N_ebits = 0;
    
    % Set the random number seed
    rand('state', seed);
    
    % Generate the transmitted symbols
    msg_bit = randi(1, N_pbits);
    symbol = QPSK_mapper(msg_bit);
    x = reshape(symbol, NT, N_frame);
    
    % Generate the channel matrices
    for i_user = 1:N_user
        H(i_user, :) = (randn(1, NT) + 1i * randn(1, NT)) / sq2;
        Channel_norm(i_user) = norm(H(i_user, :));
    end
    
    % Sort the channel matrices by channel norm
    [Ch_norm, Index] = sort(Channel_norm, 'descend');
    H_used = H(Index(1:N_act_user), :);
    
    % Calculate the BD precoding matrix
    W_bd = H_used * inv(H_used' * H_used + (mode == 1) * sigma2 * I) * H_used';
    
    % Precode the transmitted symbols
    Tx_signal = W_bd * x;
    
    % Add noise to the transmitted signal
    Rx_signal = H_used * Tx_signal + sigma * (randn(N_act_user, N_frame) + 1i * randn(N_act_user, N_frame));
    
    % Equalize the received signal
    x_hat = Rx_signal;
    
    % Reshape the equalized signal
    symbol_hat = reshape(x_hat, NT * N_frame, 1);
    
    % Slice the received symbols
    symbol_sliced = QPSK_slicer(symbol_hat);
    
    % Demap the sliced symbols
    demapped = QPSK_demapper(symbol_sliced);
    
    % Count the number of errors
    N_ebits = N_ebits + sum(msg_bit ~= demapped);
    
end

Unrecognized function or variable 'seed'.

% Calculate the BER
BER = N_ebits / N_tbits;

% Plot the BER vs. SNR
semilogy(SNRdBs, BER, '-o');
grid on;

when run this code , Error in Untitled7 (line 35)

rand('state', seed); this error show up so how can i fix it please?

[Dyuman Joshi]

"how can i fix it please?"

By defining the variable seed

Answer 1

[Cris LaPierre]

Please note that, starting in R2008b, the use of 'state' is discouraged (see here).

[Dyuman Joshi]

As Cris correctly points out, the use of input seed or state to rand is not recommended.

Use rng instead.