nargin and the if statement

Hi Im trying to understand how to use nargin but am having an issue. Hopefully someone can shed some light on. I copied this function from my text book

function z =  sqrtfun(x,y)

if (nargin==1)
   z = sqrt(x);
elseif (nargin==2)
   z = sqrt(x+y);
end

Then in another script I have put together this code to call the function

clc;
clear;
close all;

x = input('x');
y = input('y');

z = sqrtfun(x,y);

fprintf('Answer z ::: %4.2f\n', z);

The issue i'm having is that if i leave y blank no value is displayed for z. If i enter a value for x and y i get an output value for z. I don't know why this happens??

Answer 1

[Walter Roberson]

When you leave y blank in response to an input() prompt, what you get back is an empty array, and you provide that empty array as an argument. nargin tests the number of arguments passed, not what value they are, so it knows you are passing two arguments. This leads to the calculation

sqrt(x+y)

where x is not empty but y is empty. The sum of a non-empty array and an empty array is the empty array, so the result is empty.

You should modify your code to

function z =  sqrtfun(x,y)

if (nargin==1) || isempty(y)
   z = sqrt(x);
else
   z = sqrt(x+y);
end

[Sultan Al-Hammadi]

what does nargin do?

[Mukesh Mani]

nargin tests the number of arguments passed

Answer 2

[KSSV]

You change the function as follows:

function z = sqrtfun(x,varargin)
if (nargin==1) 
    z = sqrt(x); 
elseif (nargin==2) 
    y = varargin{1} ;
    z = sqrt(x+y); 
end

When you enter one value i.e. x nargin = 1 then it goes to if, if you enter two values i.e x,y nargin will be 2. y will be stored in varargin and we are calling it in else statement.

[Sultan Al-Hammadi]

what does nargin do?

and what is the functionality of "varargin{1}"?

[Steven Lord]

See the description and examples on the nargin function documentation page for more information about what it does and how to use it.

There's a documentation page for varargin as well.