creating a perfect number function

Hi. I am currently having a prob. I need to create a function that takes in the number(n) as argument and returns true if n is a perfect number. I am not allowed to use vectors and for loop for this question. I am stuck at this few codes:

function num = perfect(n)
i=1;  
sum = 0;
while i <= n/2  
if rem(n,i) == 0  
else   
i = i +1  
end  
sum = sum + i;  
end  
if n == sum   
n = true

I am a beginner in Matlab and I require assistance. Any kind soul out there to help me? Thanks!

[John D'Errico]

Using the name sum as a variable name will create problems down the road for you. Don't name variables the same as useful functions that you will later need. Or expect to see lots of bugs in your code. Of course, you might like buggy code. Your choice.

Answer 1

[Guillaume]

First and foremost, learn to use matlab's debugger. Step through your code, see how the variables change after each instruction, and check that the result was what you expected.

There is clearly a problem with your code. You have a while loop that essentially says:

while i is some value
   if some condition
      do nothing. Particularly, do not change i
   else 
      change i
   end
   do something that does not change i
end

You can see that under some condition i never changes, so the loop will repeat infinitely. You need to fix that.

As per John's comment, don't use sum as a variable name, as you won't be able to use the sum function.

Also note that

if somecondition
else
   do something
end

is better written as

if ~somecondition
   do something
end

[Fu Xiangli]

Yup I got the answer already. Apparently my initial code was rubbish. I have got the code as below:

function num = is_perfect(n)
 i = 1;
factorsum = 0;
while i<= n-1
  if rem(n,i) == 0
      factorsum = factorsum + i;
  end
  i = i +1;
end
if n == factorsum
  num = true;
else 
  num = false;
end

If there is any areas for improvement do let me know! Thank you guys!

[Guillaume]

Yes, that's much better.

One small improvement you can do is get rid of the final if and simply do:

num = n == factorsum;

Answer 2

[alex usefi]

How to get numbers like this from the code? is_perfect(6)

show result code: 1 2 3

[Guillaume]

Please start your own question rather than highjacking the answer box of an another question for something that clearly is not an answer.

Note that I would expect that a function called is_perfect to return either true or false, not a vector of numbers.