How to prevent overwrite the graph in looping?

I want to have three eyediagrams and one graph combine three while loop together. The codes is something like the below:

N=2
while (N<=4)
     . . . . . . 
eyediagram(........)

if(N==2)
      figure;
      semilogy(........);
      hold on;
      semilogy(........);
elseif (N==3)
      semilogy(........);
      hold on;
      semilogy(........);
else
      semilogy(........);
      hold on;
    semilogy(........);

       . . . . . . . 
  N=N+1;
  end

[KSSV]

Instead of plotting in conditionals....you collect the data in conditionals...and plot at once after the loops.

[Alex Phang]

Is that possible do it in the while loop?

[KSSV]

Yes very much....

Answer 1

[Birdman]

Define figure and hold on just once before while loop. It would be more efficient:

N=2;
figure;hold on;
while (N<=4)
     . . . . . . 
eyediagram(........)
if(N==2)
      semilogy(........);
      semilogy(........);
elseif (N==3)
      semilogy(........);
      semilogy(........);
else
      semilogy(........);
      semilogy(........);
       . . . . . . . 
  N=N+1;
  end

[Alex Phang]

It will produce about six blank graphs and three unwanted and unknown graphs.

[Walter Roberson]

semi_fig = figure();
semi_ax = axes('Parent', semi_fig);
hold(semi_ax, 'on')

for N = 2 : 4
  ...
  eyediagram(.....);    %always produces new figure
  if N == 2
    semilogy(semi_ax, ...)
    semilogy(semi_ax, ...)
  elseif N == 3
    semilogy(semi_ax, ...)
    semilogy(semi_ax, ...)
  elseif N == 4
    semilogy(semi_ax, ...)
    semilogy(semi_ax, ...)
  end
end

hold(semi_ax, 'off')

[Alex Phang]

@Walter Roberson, the solution that you provided is still producing the same results as above

[Walter Roberson]

You are incorrect.

semi_fig = figure();
semi_ax = axes('Parent', semi_fig);
hold(semi_ax, 'on')

x = 1 : 50;
for N = 2 : 4
  y = rand(1, 50);
  eyediagram(y, 3);    %always produces new figure
  if N == 2
    semilogy(semi_ax, x, y, 'k-');
    semilogy(semi_ax, x, sin(y), 'k*');
  elseif N == 3
    semilogy(semi_ax, x, y, 'b-');
    semilogy(semi_ax, x, y.^2, 'b*');
  elseif N == 4
    semilogy(semi_ax, x, y, 'g-');
    semilogy(semi_ax, x, cos(y), 'g*');
  end
end

hold(semi_ax, 'off')

This produces 3 eye diagrams and one graph that combines all 6 semilogy.

[Alex Phang]

This is my coding and it doesn't work just like yours.

close all; clear; clc;

semi_fig = figure();
semi_ax = axes('Parent', semi_fig);
hold(semi_ax, 'on')

for M = 2:4      % bit resolutions
Lavg=2^M;    % average symbol length
nsym=500;    % number of PPM symbols
Lsig=nsym*Lavg;    % length of PPM slots
Rb=1e6;      % bit rate
Ts=M/(Lavg*Rb);    % slot duration
Tb=1/Rb;    % bit duration

Dt =0.4;
Drms=Dt*Tb;        % RMS delay spread
a=12*sqrt(11/13)*Drms;    
nsamp=10;               % samples per symbols
Tsamp=Tb/nsamp;    % sampling time
K=30*nsamp;        % number of channel taps
k=0:K;
h=((6*a^6)./(((k*Tsamp)+a).^7));  % channel impulse response
h=h./sum(h);

EbN0=0:12;    % energy per slot
EsN0=EbN0+10*log10(M);  % energy per symbol
SNR=10.^(EbN0./10);

for ii=1:length(EbN0)
  PPM=generate_PPM(M,nsym);
  MF_out=awgn(PPM,EsN0(ii)+3,'measured');

  % hard decision decoding
  Rx_PPM_th=zeros(1,Lsig);
  Rx_PPM_th(find(MF_out>0.5))=1;
  [No_of_Error(ii) ser_hdd(ii)]=biterr(Rx_PPM_th, PPM);

  % soft decision decoding
  PPM_SDD=[];
  start=1;
  finish=2^M;
  for k=1:nsym
    temp=MF_out(start:finish);
    m=max(temp);
    temp1=zeros(1,2^M);
    temp1(find(temp==m))=1;
    PPM_SDD=[PPM_SDD temp1];
    start=finish+1;
    finish=finish+2^M;
  end
  [No_of_Error(ii) ser_sdd(ii)]=biterr(PPM_SDD,PPM);
end

Tx_signal=rectpulse(PPM,nsamp);    % Pulse shaping function (rectangular pulse)
channel_output=conv(Tx_signal,h);  % channel output
eyediagram(channel_output, 3*nsamp);
axis([-0.5 0.5 0 1]);

% theoretical calculation
Pse_ppm_hard=qfunc(sqrt(M*2^M*0.5*SNR));
Pse_ppm_soft=qfunc(sqrt(M*2^M*SNR));

if(M==2)
    semilogy(EbN0,(1/log2(M))*Pse_ppm_hard,'k-','linewidth',2);
    semilogy(EbN0,(1/log2(M))*Pse_ppm_soft,'r-','linewidth',2);
elseif (M==3)
    semilogy(EbN0,(1/log2(M))*Pse_ppm_hard,'k-X','linewidth',2);
    semilogy(EbN0,(1/log2(M))*Pse_ppm_soft,'r-X','linewidth',2);
else
    semilogy(EbN0,(1/log2(M))*Pse_ppm_hard,'k--','linewidth',2);
    semilogy(EbN0,(1/log2(M))*Pse_ppm_soft,'r--','linewidth',2);
end

grid on
legend('M=2 (HDD)','M=2 (SDD)','M=3 (HDD)','M=3 (SDD)','M=4 (HDD)','M=4 (SDD)');
xlabel('Eb/N0, dB');
ylabel('Bit Error Rate');
Title('Bit error probability curve for PPM modulation');
end

hold(semi_ax, 'off')

[Walter Roberson]

Unrecognized function or variable 'generate_PPM'.
Error in idaho (line 30)
  PPM=generate_PPM(M,nsym);

[Alex Phang]

Save this in a file named as generate_PPM.m

function PPM=generate_PPM(M,nsym)
% function to generate PPM
% 'M' bit resolution
% 'nsym': number of PPM symbol

PPM=[];
  for i= 1:nsym
    temp=randint(1,M);      % random binary number
    dec_value=bi2de(temp,'left-msb');  % converting to decimal value
    temp2=zeros(1,2^M);      % zero sequence of length 2^M
    temp2(dec_value+1)=1;      % placing a pulse according to decimal value
              % note that in matlab index does not start from zero, so need to add 1;
    PPM=[PPM temp2];      % PPM symbol
  end
end

[Walter Roberson]

You did not follow the structure I posted! When you follow the structure I posted, it works fine.