How to create a function that returns a matrix with one more popped piece randomly added and the location of it.

Hi there, I am stuck on a question and don't know how to go about it:

Write a function that given a matrix M of numbers representing locations and the number of popcorn pieces that have previously popped at each, returns a matrix with one more popped piece randomly added. In addition, the function returns the row-column coordinate where the latest piece popped.

For example

>> a = zeros(2)
a = 
  0  0
  0  0
>> aa = popcorn(a)
aa = 
  1  0
  0  0
>>[aaa rc] = popcorn(aa)
aaa
  2  0
  0  0
rc =
  1  1
>> [aaaa rc] = popcorn(aaa)
aaaa = 
  2  0
  0  1
rc = 
  2  2
>>aaaaa = popcorn(aaaa)
aaaaa = 
  2  1
  0  1

This is a homework question so a nudge in the right direction would be greatly appreciated!

Answer 1

[Roger Stafford]

Use 'randi' twice to generate random indices for the row and column and then add 1 there.

[Rohan Nair]

Hi Roger, I have tried this approach and this is the code i have so far.

function output  = popcorn(M)
[w, z] = size(M);
a = randi(w);
b = a+1;
f = randi(z);
g = f+1;
output = [b, g];

This is a start i have so far, though it only gives me random numbers for the size of the matrix. Any other help would be greatly appreciated!

[Image Analyst]

Rohan, you don't add 1 to the random row and column you get. You're supposed to add 1 to the value of w at that row and column, that is, w(a, f). Try again.

[Rohan Nair]

Hi there, Sorry to bother you again but I have tried this for so long now and still cant seem to get it. I have taken your advice and this is what is was able to come up with. function output = popcorn(M) [w, z] = size(M); a = randi(w); f = randi(z); b = w(a+1,f+1); output = b; end

But now when I run the code it now says

Attempted to access w(3,3); index out of bounds because numel(w)=1.

Error in popcorn (line 5) b = w(a+1,f+1);

Not sure how this happened.

Thank you for your help and time!

[Stephen23]

You are still adding one to each of the indices, and not to the value at that location. Look at the code w(a+1,f+1): a is an index, and then you add one to it. This is not the aim of your task! Image Analyst told you to not do this, but instead to "add 1 to the value of w at that row and column, that is, w(a, f). Try again." Note that Image Analyst even told you what you should be adding one to: w(a,f).

Try again!

[Rohan Nair]

Thank you Stephen for clarifying that! What i have done now is exactly what you said and also change w(a,f) to M(a,f)+ 1 as i need to index into the original matrix. This is the new code so far:

function output  = popcorn(M)
  [w, z] = size(M);
  a = randi(w);
  f = randi(z);
  b = M(a,f)+1;
  output = b;
end

Though now I only get a single value and now I'm wondering how to input that into the original matrix and keep 'popping pieces' in my matrix. Thank you for your help and time!

[Image Analyst]

You need to declare a second output argument, rowAndColumn

function [output, rowAndColumn] = popcorn(M)

Now, what do you think, looking over your variables, rowAndColumn might be?

rowAndColumn  = ??????

By the way, your "b" is totally unnecessary. And even worse , it's totally wrong . It needs to be the whole matrix, not just the one element. Keep trying.

[Rohan Nair]

Okay thank you, after a lot of thinking and reading what you said this is the new code, though it only gives a 1x2 matrix and not the matrix i need as per the example: function [output, rowAndColumn] = popcorn(M) [w, z] = size(M); a = randi(w); f = randi(z); rowAndColumn = [w,z]; output = [a,f]; end

I feel I'm getting closer to the answer yet i still feel so lost.