I need help writing a matlab function
显示 更早的评论
I need help writing a Matlab function that takes a positive integer n as its argument, and returns the sum of all odd numbers between 1 and n.
1 个评论
Jan
2017-1-15
Please clarify, if this is your homework. If so posting a solution might be counter-productive, because you would cheat if you deliver it. Even if it is a homework question, posting what you have tried so far and asking a specific question would be useful. Because asking for explanations is not a cheating instead of letting others solve your work.
采纳的回答
John BG
2017-1-13
Hi Mateo
what about this
function sn=sum_odds(n)
narginchk(1,1);
if(n<0) || (n==0)
error(message('input error n<=0'));
end
if abs(n-floor(n))>0
error(message('input not +int'));
end
sn=sum([1:2:n])
% if rem(n,2)==0
% sn=sum([1:2:n-1])
% end
%
% if rem(n,2)>0
% sn=sum([1:2:n])
% end
end
if you find these lines useful would you please mark my answer as Accepted Answer
To any other reader, if you find this answer of any help please click on the thumbs-up vote link,
thanks in advance for time and attention
John BG
5 个评论
Walter Roberson
2017-1-13
You just gave complete code for a homework question :(
Image Analyst
2017-1-14
That assumes it was a homework question. Mateo did not say it was a homework question, either in the body of the message or via a tag. It may well be, but should we assume that? Maybe it's not. Or maybe he's self-learning and this is not a question to be turned in and graded. Every time someone posts something should they say "This is not a homework question" if it is not? A given question might be assumed to be a homework question by some people and not a homework question by other people. I guess it's up to each individual's judgment.
@Image Analyst: You are right. I've removed my comment, which mentioned http://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers.
For me the question sounds like a homework or Cody problem. Even if this does not concern the OP, this thread is found when others pupils search in the net. Beside this, the OP does not show any own effort like posting code or asking for a specific detail. Therefore I judge that this is a "do-it-for-me" question, which I do not like to answer with code also.
Walter Roberson
2017-1-15
Should we assume that it is a homework question: Yes. Nothing is lost by assuming that for something that looks like homework. The person who posted the question can also provide clarification afterwards that might potentially lead to someone posting a more complete solution, but an overcomplete solution cannot be withdawn.
更多回答（2 个）
Jan
2017-1-13
3 个投票
Do you remember how Gauss calculated the sum over all elements from 1 to n? You can modify the method to use only the pairs of odd numbers. This reduces the compuations drastically and you should never process the dull sum.
3 个评论
@John BG: note that square brackets are not required: sum(1:1:100).
The mlint messages is ""Use of brackets [] is unnecessary." This might also be of interest:
I do not post the solution, because I assume, that this is a homework question. I even did not mention, that asking an internet search engine for the terms "sum of odd numbers" reveals the main part of the solution already: The sum of N odd numbers is N^2.
@Stephen: The step size 1 is not required in vectors, so this is enough: sum(1:100). This does not influence the computing time but is nicer . The leaner the code, the less chances for a typo... :-)
Walter Roberson
2017-1-15
Assuming N odd,
1 + 3 + 5 +... N
N + (N-2) + (N-4) +... 1
Each pair adds to N+1. Count the pairs and multiply by that. Then divide by 2 because each pair is being counted twice.
类别
在 帮助中心 和 File Exchange 中查找有关 Function Creation 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
