Asked by Caitlin Schmidt
on 21 Jul 2019

This is what I have so far:

function week7hw1(pixels, varargin)

%This function will receive the size of the pixels as an input

%if a second input is entered, the image will be the colormap

n=nargin;

mat=randi(pixels);

if n==0

image(mat)

elseif n==1;

colormap(varargin)

image(mat)

end

end

I'm not sure what I am doing wrong for this function.

Answer by John D'Errico
on 21 Jul 2019

Edited by John D'Errico
on 21 Jul 2019

Accepted Answer

Your problem is that you misunderstand nargin.

By way of example, I wrote this very simple function.

function week7hw1(pixels, varargin)

nargin

numel(varargin)

So all it does is write out the number of elements in varargin, as well as write out the value of nargin. Now I'll try it out.

week7hw1(1,2)

ans =

2

ans =

1

Hmm. there were two inputs to the function.

Nargin was 2. But numel(varargin) was 1, as expected.

So, what does nargin do? It is NOT the number of elements in varargin. nargin is the TOTAL number of input arguments to the function. Similarly, if I provide no second argument, then what happens?

week7hw1(1)

ans =

1

ans =

0

Again, I provided no second argument. nargin was 1, since there was ONE argument. varargin was an empty array this time.

So, why does your code fail? You test to see if nargin is ZERO or ONE. But nargin will always be at least 1, because you always are providing the first argument. So you want to distinguish if there are 1 or 2 arguments provided. The necessary fix to your code is very simple.

Caitlin Schmidt
on 21 Jul 2019

This has helped and I change what n is equal to. Now, I try to run the function with two inputs and I am receiving an error with colormap(varargin). Do you know what I may do to fix this?

Thank you!

John D'Errico
on 21 Jul 2019

That part is easy. varargin is a CELL array. This happens because your additional arguments may be all sorts of things. So it must contain anything. But colormap cannot take a cell array as input. Instead, you need to extract that element from the cell array.

colormap(varargin{1})

You index a cell array using {} curly braces, in order to extract an element of that array. So the line as I wrote it extracts the first element of varargin, then passes that into colormap.

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Answer by KALYAN ACHARJYA
on 21 Jul 2019

Edited by KALYAN ACHARJYA
on 21 Jul 2019

function image1=rand_image()

pixel_num=input('Enter the value ');

image1=logical(randi(2,[pixel_num pixel_num])-1); %@Image Analyst Answer

imshow(image1);

end

Command Window:

>> y=rand_image();

Enter the value 100

Figure Window:

Second Part is not complete-

If a second input argument is provided, it will

Caitlin Schmidt
on 21 Jul 2019

KALYAN ACHARJYA
on 21 Jul 2019

function image1=rand_image(pixel_num)

image1=logical(randi(2,[pixel_num pixel_num])-1); %@Image Analyst Answer

imshow(image1);

end

Now pass the pixel value from here

y=rand_image(100)

Caitlin Schmidt
on 21 Jul 2019

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