Selective parameters in MATLAB functions

1. Write it at the front

A lot of MATLAB Functions support optional input parameters and output parameters . for example , We call plot function , Input parameters can be as few as 2 individual , You can have as many as 7 Parameters . On the other hand , function max It supports one output parameter , Two output parameters are also supported . If there is only one output parameter ,max The maximum value of the function will be returned . If there are two output parameters, it will return the maximum value of the array and the location of the maximum value . How to know a MATLAB Function has several input and output parameters , And the corresponding functions of the function ？

stay MATLAB There are eight special functions in to get information about selective parameters and to report errors in these parameters . Here is an introduction .

2. Meaning of optional parameters

Parameters	meaning
nargin	Returns the number of actual input parameters required to call this function
nargout	Returns the number of actual output parameters required to call this function
nargchk	If you want a function call to be called with too many or too few parameters , that nargchk Function will return a standard error message
error	Display error message , And stop the function to avoid this error . If the parameter error is fatal , This function will be called .
warning	Display a warning message and continue to execute the function , If the parameter error is not fatal , Execution can continue , Then this will be called .
inputname	Returns the actual variable name for a specific number of parameters .

3. Examples of functions written with optional parameters

function [mag, angle] = polar_value(x, y) 
% POLAR_VALUE Converts(x, y) to (r, theta) 
% Punction POLAR_VALUE converts an input(x,y) 
% va1ue into (r, theta), with theta in degrees. 
% It illustrates the use of optional arguments. 
% Define variables: 
% angle --Angle in degrees 
% msg --Error message 
% mag --Magnitude 
% x --Input x value 
% y --Input y value(optional) 
% Record Of revisions: 
% Date Programmer Description of change 
% ======== ============== ======================== 
% 12/16/98 S.J.Chapman Original code 
% Check for a legal number of input arquments 

%  among  min_args  It refers to the minimum number of parameters ,max_args  Is the maximum number of indices ,num_args  It refers to the actual number of parameters . If the number of parameters is not within the allowable range , A standard error message will be generated . If the number of parameters is within the allowable range , Then this function will return a null character .
msg = nargchk(1,2,nargin); 

%  function  error  It is a standard way to display standard error messages and to abort custom functions that cause error messages .
error(msg); 

% If the y argument is missing, set it to 0. 
%  If there is only one parameter , Then the function assumes  y  The value is  0
if nargin < 2 
	y = 0; 
end 

% Check for (0,0) input argument, and print out 
% a warning message. 
% x and y All are 0 The situation of , Output warning messages 
if x == 0 & y == 0 
	msg = 'Both x and y are zero: angle is meaningless!'; 
	warning(msg); 
end 
% Now calculate the magnitude 
mag = sqrt(x .^2 + y .^2); 

% If the second output argument is present,calculate 
% angle in degrees 
if nargout == 2 
	angle = atan2(y,x) * 180/pi; 
end

test ：

1. No parameters entered

>> [mag angle]=polar_value

??? Error using ==> polar_value 
Not enough input arguments. 

2. Too many parameters entered

>> [mag angle]=polar_value(1,-1,1)

??? Error using ==> polar_value 
Too many input arguments. 

3. Enter a parameter

>> [mag angle]=polar_value(1)

mag = 
 1 
angle = 
 0 

4. Enter two parameters

>> [mag angle]=polar_value(1,-1)

mag = 
 1.4142 
angle = 
 -45 

5. Output a parameter

>> mag = polar_value(1,-1)

mag = 
 1.4142 

6. Input x=0,y=0 Parameters

>> [mag angle] = polar_value(0,0) 

Warning: Both x and y are zero: angle is meaningless! 
> In polar_value at 27 
mag = 
 0 
angle = 
 0 

Deepen the understanding of function writing through the above examples , Understand the meaning of each parameter , Notes extracted from ：

[1] S.J.Chapman《MATLAB Programming 》 Chinese version