what dose [1: equations : 0] means in MATLAB?

Hello;

I currently find a code to draw signal spectrogram of the signal, I got a quite good result from the signal using their given signal, but it cannot work for my own signal, I feel so confused about one code: f=[0:nhaf -nhaf+1-odvn:-1]/N; Can I ask what is that means and why it always be an empty mitrax when I try to use it for my own signal? The code and signal of the example are shows below:

SampFreq = 1000;
t = 0: 1/ SampFreq :1;
LFM_K0 = -50.34;
LFM_f0 =100.23;
LFM_A0 = exp(-0.5*t);
Sig = LFM_A0 .*cos(2*pi*(LFM_f0*t+(LFM_K0/2)*t.^2));
SNR0 =20;
ST = stran(Sig);
imagesc(t,SampFreq,abs(ST));
axis xy;

function ST=stran(h)
% Compute S-Transform without for loops
%%% Coded by Kalyan S. Dash %%%
%%% IIT Bhubaneswar, India %%%
[~,N]=size(h); % h is a 1xN one-dimensional series
nhaf=fix(N/2);
odvn=1;
if nhaf*2==N;
    odvn=0;
end
f=[0:nhaf -nhaf+1-odvn:-1]/N;
Hft=fft(h);
%Compute all frequency domain Gaussians as one matrix
invfk=[1./f(2:nhaf+1)]';
W=2*pi*repmat(f,nhaf,1).*repmat(invfk,1,N);
G=exp((-W.^2)/2); %Gaussian in freq domain
% End of frequency domain Gaussian computation
% Compute Toeplitz matrix with the shifted fft(h)
HW=toeplitz(Hft(1:nhaf+1)',Hft);
% Exclude the first row, corresponding to zero frequency
HW=[HW(2:nhaf+1,:)];
% Compute Stockwell Transform
ST=ifft(HW.*G,[],2); %Compute voice
%Add the zero freq row
st0=mean(h)*ones(1,N);
ST=[st0;ST];
end

[Walter Roberson]

Be cautious with spacing

f=[0:nhaf -nhaf+1-odvn:-1]/N;

means

f=[0:nhaf, -nhaf+1-odvn:-1]/N;

but if you were to try modifying the line for your own purposes, it would be easy to slip and enter either

f=[0:nhaf-nhaf+1-odvn:-1]/N;

or

f=[0:nhaf - nhaf+1-odvn:-1]/N;

which would both mean

f=[0:(nhaf-nhaf+1-odvn):-1]/N;

[Jingyi Yuan]

That's amazing! Thank you so much!

And I have tried again, meet another problem (happened several times) "Requested 152064x304128 (344.6GB) array exceeds maximum array size preference (7.8GB). This might cause MATLAB to become unresponsive." my signal arry is 304128*1, I know it is quite big data arry, can I ask how to sove that problems? Thank you for helping!

[Rik]

Let's make the sizes smaller so we can see what is happening:

signal=reshape(1:6,[],1);%create column vector
array=SomeFunctionWithImplicitExpansion(signal)

array = 6×3

1 2 3 2 4 6 3 6 9 4 8 12 5 10 15 6 12 18

function array=SomeFunctionWithImplicitExpansion(signal)
x=signal(1:(end/2)).';%select first half and transpose
array=signal.*x;%multiply element-wise
end

As you can see, the array size goes from 6 to 18, taking up tripple the space.

Now imagine doing that with your signal. You should rethink your strategy of whatever computation you're doing to split it up.

[Jingyi Yuan]

That's so helpful thank you so much! And I was wondering if the downsample is an appoparate way to dectease the signal size?

Answer 1

[Rik]

In addition to the comment from Walter:

Your question can be answered by two searches in the documentation:

doc MATLAB Operators and Special Characters

Or (since I happen to know which specific page you need):

doc colon

 :  Colon.
    J:K  is the same as [J, J+1, ..., J+m], where m = fix(K-J). In the 
    case where both J and K are integers, this is simply [J, J+1, ..., K]. 
    This syntax returns an empty matrix if J > K.
 
    J:I:K  is the same as [J, J+I, ..., J+m*I], where m = fix((K-J)/I). 
    This syntax returns an empty matrix when I == 0, I > 0 and J > K, or 
    I < 0 and J < K.
 
    COLON(J,K) is the same as J:K and COLON(J,I,K) is the same as J:I:K.
 
    The colon notation can be used to pick out selected rows, columns
    and elements of vectors, matrices, and arrays.  A(:) is all the
    elements of A, regarded as a single column. On the left side of an
    assignment statement, A(:) fills A, preserving its shape from before.
    A(:,J) is the J-th column of A.  A(J:K) is [A(J),A(J+1),...,A(K)].
    A(:,J:K) is [A(:,J),A(:,J+1),...,A(:,K)] and so on.
 
    The colon notation can be used with a cell array to produce a comma-
    separated list.  C{:} is the same as C{1},C{2},...,C{end}.  The comma
    separated list syntax is valid inside () for function calls, [] for
    concatenation and function return arguments, and inside {} to produce
    a cell array.  Expressions such as S(:).name produce the comma separated
    list S(1).name,S(2).name,...,S(end).name for the structure S.
 
    For the use of the colon in the FOR statement, See FOR.
    For the use of the colon in a comma separated list, See VARARGIN.

    Documentation for colon
       doc colon

    Other functions named colon

       codistributor1d/colon      distributed/colon    gpuArray/colon
       codistributor2dbc/colon    dlarray/colon        sym/colon
       datetime/colon             duration/colon

[Jingyi Yuan]

That's very useful! Thank you so much!

[Rik]

You're welcome. If this answered your question, please consider marking it as accepted answer.