Help in numerical exercise

2014 5 1
2 个回答
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更新时间：2014 5 2
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0 个投票

Hi everyone,
I have a vector y2 starting from 1 to 100 with properties of y2(1)=1 and y2(i+1)-y2(i)=i+1
Knowing that i=1,…,99 what it will be y2(100)?
Thank you very much!!!
Best Regards.

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Roger Stafford
Roger Stafford 2014-5-2
编辑：Image Analyst 2014-5-2

1 个投票

If you look at this site in the section called Anecdotes" you will see a short cut to obtaining your answer. It doesn't require matlab at all.
http://en.wikipedia.org/wiki/Carl_Friedrich_Gauss

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Image Analyst
Image Analyst 2014-5-2
I don't get 5050, because in Tamer's situation, the difference between two terms is not 1 but (i+1), so I get a different number. The difference between adjacent numbers increases as the number of terms grows, unless Tamer didn't transcribe it correctly. y2(2) and y2(1) are separated by 1+1 = 2 while y2(100) and y2(99) are separated by 99+1 = 100.
Star Strider
Star Strider 2014-5-2
I do get 5050, rearranging the equation to have y2(i+1) on the LHS, then looping.
Gauss’ ‘shortcut’ solution is brilliant and insightful. But then, so was Gauss.
Strider
Strider 2014-5-2
Hi Star Strider, I am a novice in Matlab, can you please show me what you typed to get the right answer (5050). thanks a lot!!
Image Analyst
Image Analyst 2014-5-2
You're right. I messed up.

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Image Analyst
Image Analyst 2014-5-2
编辑：Image Analyst 2014-5-2

0 个投票

Why not make a simple for loop and find out?
y2(1)=1;
for i = 1 : 99
y2(i+1) =
and so on.... It's the best way to learn!

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