narginchk and varargin in MATLAB

I have come across PART of a code in MATLAB in a toolbox that I don't understand

    elseif (txMode==2) 

    narginchk(7, 7);
    numTx = varargin{1};
    numRx = varargin{2};

    switch numTx
        case 2    
            numCSRRE_RB = 4*2*2; 
        case 4      
            numCSRRE_RB = 4*3*2; 
    end

I don't understand what `narginchk` and `varargin` are used for in this example, and why is that the output of `varargin{1}` would be either 2 or 4 (a conclusion I came up with when looking at the code after `switch`).

Thanks

Answer 1

[James Tursa]

narginchk(7, 7) throws an error if the number of input arguments is less than 7 or greater than 7 (i.e., the number of input arguments must be exactly 7 in this case or an error will be thrown).

varargin{1} is the first input argument.

varargin{2} is the second input argument.

Why the value of varargin{1} should be 2 or 4 would depend on the code in question and how it is called.

Answer 2

[Lei]

Recode

function p= marie (p,q)
narginchk[2,3]
disp('Yo, G!')
a=p+q
end

[Walter Roberson]

%if the user passes in no parameters then none of the parameters will exist
%if the user passes in too few parameters then variable p will not exist
%if the user passes in more than 3 parameters then there will be a 4th
%parameter and that should be rejected
%
%note that we are accepting a third parameter even though we do not do
%anything with it. This is because the original code permitted either 2 or
%3 inputs.
function p = marie (p,q,extra_ok,extra_not_ok)
    if ~exist(p, 'var') || exist('extra_not_ok', 'var')
        error('You must pass in either 2 or 3 inputs')
    end
    disp('Yo, G!')
    a=p+q
end