creating a perfect number function

Question

Fu Xiangli 2016-8-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/301380-creating-a-perfect-number-function

编辑： Guillaume 2018-9-10

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!

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

John D'Errico 2016-8-30

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.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Guillaume 2016-8-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/301380-creating-a-perfect-number-function#answer_233150

在 MATLAB Online 中打开

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

2 个评论
显示无隐藏无

Fu Xiangli 2016-8-31

在 MATLAB Online 中打开

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