Index exceeds the number of array elements (4)

I keep running into the same error for my functions. The error and functions (uniquan.m and sampandquant.m) are shown below:

>> Exsample
Index exceeds the number of array elements (4).

Error in uniquan (line 19)
q_out=q_level(qindex);  % use index vector to generate output

Error in sampandquant (line 21)
    [sq_out,Delta,SQNR]=uniquan(s_out,L);

Error in Exsample (line 12)
[s_out,sq_out,sqh_out,Delta,SQNR]=sampandquant(xsig,16,td,ts);
 

Here is my function:

% (Exsample.m)
% Example of sampling, quantization and zero-order hold
clear;clf;
td=0.002;       %origional sampling rate 500 Hz
t=[0:td:1.];    %time interval of 1 second
xsig=sin(2*pi*t)-sin(6*pi*t);   % 1Hz+3Hz sinusoids
Lsig=length(xsig);

ts=0.02;        %new sampling rate = 50Hz.
Nfactor=ts/td;
% send the signal through a 16-level uniform quantizer
[s_out,sq_out,sqh_out,Delta,SQNR]=sampandquant(xsig,16,td,ts);
%   receive 3 signals
%       1. sampled signal s_out
%       2. sampled and quantized signal sq_out
%       3. sampled, quantized, and zero-order hold signal sqh_out
%
%   Calculate the Fourier Transfoms
Lfft=2^ceil(log2(Lsig)+1);
Fmax=1/(2*td);
Faxis=linspace(-Fmax,Fmax,Lfft);
Xsig=fftshift(fft(xsig,Lfft));
S_out=fftshift(fft(s_out,Lfft));

And I'm drawing from:

% (uniquan.m)
function [q_out,Delta,SQNR]=uniquan(sig_in,L)
%   Usage
%   [q_out,Delta,SQNR]=uniquan(sig_in,L)
%   L   -   number of uniform quantization levels
%   sig_in  -   input signal vector
%   Function outputs:
%       q_out   -   quantized output
%       Delta   -   quantization interval
%       SQNR    -   actual signal to quantization noise ratio
sig_pmax=max(sig_in);   % finding the positive peak
sig_nmax=min(sig_in);   % finding the negative peak
Delta=(sig_pmax-sig_nmax)/L;    % quantization interval
q_level=sig_nmax+Delta/2:sig_pmax-Delta/2;  % define Q-levels
L_sig=length(sig_in);   % find signal length
sigp=(sig_in-sig_nmax)/Delta+1/2;   % convert into 1/2 to L+1/2 range
qindex=round(sigp);     % round to 1,2, ... L levels
qindex=min(qindex,L);   % eliminate L+1 as a rare possibility
q_out=q_level(qindex);  % use index vector to generate output
SQNR=20*log10(norm(sig_in)/norm(sig_in-q_out)); % actual SQNR value
end

And:

% (sampandquant.m)
function [s_out,sq_out,sqh_out,Delta,SQNR]=sampandquant(sig_in,L,td,ts)
%   Usage
%       [s_out,sq_out,sqh_out,Delta,SQNR=sampandquant(sig_in,L,td,ts)
%   L   -   number of uniform quantization levels
%   sif_in  -   input signal vector
%   td  -   origional signal sampling period of sig_in
%   ts  -   new sampling period
% NOTE: td*fs must be a positive integer;
%   Function outputs:
%           s_out   -   sampled output
%           sq_out  -   sample-and-quantized output
%           sqh_out -   sample, quantize, and hold output
%           Delta   -   quantization interval
%           SQNR    -   actual signal to quantization noise ratio

if (rem(ts/td,1)==0)
    nfac=round(ts/td);
    p_zoh=ones(1,nfac);
    s_out=downsample(sig_in,nfac);
    [sq_out,Delta,SQNR]=uniquan(s_out,L);
    s_out=upsample(s_out,nfac);
    sqh_out=kron(sq_out,p_zoh);
    sq_out=upsample(sq_out,nfac);
else
    warning('Error! ts/td is not an integer!')
    s_out=[];sq_out=[];sqh_out=[];Delta=[];SQNR=[];
end
end

Answer 1

[Sudheer Bhimireddy]

Try debugging by placing breakpoints inside the functions.

Here is what I see. Your q_level array is size 1x4 while the q_index has a size 1x51 or signal length is 51. You may want to define sufficient Q-levels in order to use q_level(qindex).

[Zach Fisher]

Becasue of your comment, I was able to debug and get the error corrected. Thank you so much.

[Fares Saleh]

Please can you show me what is the part you corrected so ican apply it because i have the same problem

Thank you