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Index exceeds the number of array elements (4)

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Zach Fisher
Zach Fisher on 9 Aug 2020
Commented: Zach Fisher on 9 Aug 2020
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

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Answers (1)

Sudheer Bhimireddy
Sudheer Bhimireddy on 9 Aug 2020
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).

  1 Comment

Zach Fisher
Zach Fisher on 9 Aug 2020
Becasue of your comment, I was able to debug and get the error corrected. Thank you so much.

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