I need help writing a matlab function

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Mateo Kurkuti
Mateo Kurkuti 2017-1-13
编辑： Jan 2017-1-15
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
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.

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采纳的回答

John BG
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
<mailto:jgb2012@sky.com jgb2012@sky.com>
  5 个评论
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Jan
Jan 2017-1-15
编辑：Jan 2017-1-15
@John BG: The message() command "is intended for MathWorks use only" according to the documentation. In addition it requires a qualified message-ID, therefore your error handling causes another error.
Walter Roberson
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.

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更多回答（2 个）

Walter Roberson
Walter Roberson 2017-1-13
Jan
Jan 2017-1-13
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
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Jan
Jan 2017-1-15
编辑：Jan 2017-1-15
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
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.

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