Please Can some one fix this code? I am unable to understand this code? Though fixing one problem another problem is arising !

% Parameters
Np = 2; % Number of reflecting elements in IRS
K = 2; % Number of users
Mtot = 20:20:120; % Total number of antennas at the base station
Pmax = 10; % Maximum transmit power
fc = 28e9; % Carrier frequency
fd = 200; % Maximum Doppler shift
%N = 100; % Number of IRS size values to simulate
Np = 2; % IRS size values to simulate
SNR_dB = 20; % SNR in dB
SNR = 10^(SNR_dB/10); % SNR in linear scale
% Generate channel matrices
for i=1:length(Mtot)
H = (randn(Mtot(i),K)+1j*randn(Mtot(i),K))/sqrt(2);
G = (randn(Np,Mtot(i))+1j*randn(Np,Mtot(i)))/sqrt(2);
F = (randn(Mtot(i),K)+1j*randn(Mtot(i),K))/sqrt(2);
% Simulate achievable sum rate vs IRS size
sum_rate_fc = zeros(1,Mtot(i));
sum_rate_fd = zeros(1,Mtot(i));
sum_rate_zf = zeros(1,Mtot(i));
    G = (randn(Np,Mtot(i))+1j*randn(Np,Mtot(i)))/sqrt(2);
    H_irs = H*G;
    H_eff_fc = H_irs;
    H_eff_fd = H_irs.*exp(-1j*2*pi*fd*(0:K-1).'/fd);
    H_eff_zf = H_irs*(H_irs'*H_irs)^(-1)*H_irs';
    sum_rate_fc = sum(log2(1+SNR*abs(H_eff_fc*F).^2));
    sum_rate_fd = sum(log2(1+SNR*abs(H_eff_fd*F).^2));
    sum_rate_zf = sum(log2(1+SNR*abs(H_eff_zf*F).^2));
end

Arrays have incompatible sizes for this operation.

% Plot achievable sum rate vs IRS size
figure;
plot(Np_values,sum_rate_fc,'-o','LineWidth',2,'MarkerSize',8);
hold on;
plot(Np_values,sum_rate_fd,'-s','LineWidth',2,'MarkerSize',8);
plot(Np_values,sum_rate_zf,'-d','LineWidth',2,'MarkerSize',8);
xlabel('Number of reflecting elements in IRS (Np)');
ylabel('Achievable sum rate (bps/Hz)');
legend('Proposed fc','Proposed fd','ZF+ Random PBF');
% Simulate achievable sum rate vs Pmax
P_values = 0:0.1:Pmax;
sum_rate_proposed = zeros(1,length(P_values));
for i = 1:length(P_values)
    P = P_values(i);
    [W,~,~] = proposed_algorithm(P,H,G,F,Np,K);
    sum_rate_proposed(i) = sum(log2(1+SNR*abs(H_eff_fc*W).^2));
end
% Plot achievable sum rate vs Pmax
figure;
plot(P_values,sum_rate_proposed,'-o','LineWidth',2,'MarkerSize',8);
xlabel('Maximum transmit power (Pmax)');
ylabel('Achievable sum rate (bps/Hz)');
% Plot convergence behavior of the proposed algorithm
figure;
[~,rate,~] = proposed_algorithm(Pmax,H,G,F,Np,K);
plot(rate,'-o','LineWidth',2,'MarkerSize',8);
xlabel('Iteration');
ylabel('Achievable sum rate (bps/Hz)');

expected output plots

[per isakson]

You cannot multiply a 1x2 vector by a 20x20 array

K>> H_eff_fd = H_irs.*exp(-1j*2*pi*fd*(0:K-1).'/fd);
Matrix dimensions must agree. 
K>> z = exp(-1j*2*pi*fd*(0:K-1).'/fd)
z =
1 +          0i
1 + 2.4493e-16i
K>> whos z H_irs
Name        Size            Bytes  Class     Attributes
H_irs      20x20             6400  double    complex   
z           2x1                32  double    complex   

K>>