varargin

It is used for situations where you want to allow any number of input arguments (so you can't list them). A common reason for that is optional settings -- in MATLAB this is often done with property name/property value pairs. For example, think of how you can pass extra options to plot:

plot(x,y) % plain
plot(x,y,'LineWidth',4)
plot(x,y,'Marker','o','LineWidth',2)
plot(x,y,'Marker','o','LineWidth',2,'MarkerFaceColor','r')

etc. Here you don't want to force the user to input all the possible optional parameters in a specific order, so instead you allow them to specify 'MagicPropertyName' takes the value PropertyValue (eg 'LineWidth' takes the value 2).

To write a function that can do this, you'd make a function declaration like

function plot(x,y,varargin)

Then inside this function, x takes the value of the first input, y takes the value of the second, and all the rest go into cells of the cell array varargin. So, in the last example, varargin would be a 1-by-6 cell array; varargin{1} would be the string 'Marker', varargin{4} would be the number 2, etc.

So obviously there's a bunch of programming you have to do as the developer to parse the elements of varargin, and make your code behave accordingly.

I don't really understand the last question. Could you elaborate?

(Note: the actual plot function is actually even more flexible than this -- the above function declaration line is for illustration only.)

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Walter Roberson 2012-2-14

You cannot pass adaptfilt.lms objects around in Simulink . No efforts along the line of calling lms.m directly are going to work.

Walter Roberson 2012-2-14

Alternatives discussed in one of your other Questions.

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Answer 3

Benjamin Schwabe 2012-2-14

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varargin is used when the number of input parameter might change. Basically, it puts all input arguments into a cell array. The number of input parameters is given by

nargin.

You can access any of the input values inside the function by

varargin{ind}

where ind is the index number of your argument.