What are these commands in Matlab? Can any one explain them with examples. I searched them but didn't find any help

I don't understand the following commands in Matlab. I searched their help but in vain. Can anyone explain them with examples?

M = metadata.iqDAC.';
downsamp = metadata.fs_iqDAC/metadata.fs_iqADC;
squeeze
hanning
fftshift

Answer 1

[Rik]

The first line is accessing a field iqDAC of the struct metadata, which it transposes.

The second line divides two variables.

%you can also use doc instead of help
help squeeze

 SQUEEZE Remove singleton dimensions.
    B = SQUEEZE(A) returns an array B with the same elements as
    A but with all the singleton dimensions removed.  A singleton
    is a dimension such that size(A,dim)==1.  2-D arrays are
    unaffected by squeeze so that row vectors remain rows.
 
    For example,
        squeeze(rand(2,1,3))
    is 2-by-3.
 
    See also SHIFTDIM.

    Documentation for squeeze
       doc squeeze

    Other functions named squeeze

       distributed/squeeze    dlarray/squeeze    tall/squeeze

help hanning

 HANNING   Hanning window.
    HANNING(N) returns the N-point symmetric Hanning window in a column
    vector.  Note that the first and last zero-weighted window samples
    are not included.
 
    HANNING(N,'symmetric') returns the same result as HANNING(N).
 
    HANNING(N,'periodic') returns the N-point periodic Hanning window,
    and includes the first zero-weighted window sample.
 
    NOTE: Use the HANN function to get a Hanning window which has the 
           first and last zero-weighted samples. 
 
    See also BARTLETT, BLACKMAN, BOXCAR, CHEBWIN, HAMMING, HANN, KAISER
    and TRIANG.

help fftshift

 FFTSHIFT Shift zero-frequency component to center of spectrum.
    For vectors, FFTSHIFT(X) swaps the left and right halves of
    X.  For matrices, FFTSHIFT(X) swaps the first and third
    quadrants and the second and fourth quadrants.  For N-D
    arrays, FFTSHIFT(X) swaps "half-spaces" of X along each
    dimension.
 
    FFTSHIFT(X,DIM) applies the FFTSHIFT operation along the 
    dimension DIM.
 
    FFTSHIFT is useful for visualizing the Fourier transform with
    the zero-frequency component in the middle of the spectrum.
 
    Class support for input X:
       float: double, single
 
    See also IFFTSHIFT, FFT, FFT2, FFTN, CIRCSHIFT.

    Documentation for fftshift
       doc fftshift

    Other functions named fftshift

       codistributed/fftshift

[Sadiq Akbar]

Thank you very much for your kind response. What is metadata and where does this data come from? And how will we know that this data has these fields such as iqDAC etc.?

About the remaing lines, yes this is the help but its in vain for me as I don't understand them. So can you explain them with simple examples?

[Walter Roberson]

It is possible that metadata is a class and you are accessing obscure static methods for the class.

It is possible that metadata is a class and you are access class variables for the class.

It is possible that metadata is an object of some class and you are accessing properties or methods of the class. It might be a java object. Possibly an object returned by parsing XML.

It is possible that metadata is a package and metadata.iqDAC is a function (with no arguments) in the class.

It is possible that metadata is a MATLAB struct.

We do not know where it came from. I searched the internet, but I was not able to find any matches for it. It is not anything offered by Mathworks.

To see what fields of a struct are available, you can use fieldnames()

You can see a list of properties of an object by using properties() [you might possibly not see some hidden properties.]

[Walter Roberson]

t = linspace(0, 10, 500);
y = 3*sin(6*pi*t + 1/10) + cos(5*pi*t - 1/20);
plot(t, y); title('signal')

fy = fft(y);
plot(abs(fy)); title('fft of signal');

fft of a real signal always has two halves, one that sort of corresponds to positive frequencies, and one that sort of corresponds to negative frequencies. Notice from the fft plot that the two halves are reflections of each other around the center.

fys = fftshift(fy);
plot(abs(fys)); title('fftshift')

Notice that the right half of the fft has been moved to the left. Although not labeled correctly in this example, the "0" frequency is now in the middle of the fft shift graph, and positive frequencies are to the right and negative frequencies are to the left.

[Sadiq Akbar]

Thank you very much for your so much comprehensive explanation. As you told that the 0 frequency is in the middle of the fft shift. So I don't see. If the x-axis is frequency axis, then values of x-axis remains the same. However the two spikes have been shifted and reflected. Also what is the y-axis in the fft shift graph?

[Walter Roberson]

I did not bother to label the axes properly.

[Sadiq Akbar]

ok thanks a lot for your kind reply.

[Sadiq Akbar]

Dear Walter Roberson I want to accept your answer but "Accept this answer" is not in front of your reply. So what should I do to accept your answer?

[Steven Lord]

A comment (the responses you, Walter, and I have written to Rik's answer are all comments) is not an answer and so cannot be accepted like an answer can.

[Sadiq Akbar]

Ok thank you very much for your guidance.

[Walter Roberson]

Rik did the basic explaining; I described less than you could see in the first example of fft; https://www.mathworks.com/help/matlab/ref/fft.html#buuutyt-7

[Sadiq Akbar]

Thanks for your help as well as for the help of Rik.