- #1

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What is the average of (Ri-1/N*Sum[Ri])^2 The sum is from i=1 to i=N.

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- #1

- 33

- 0

What is the average of (Ri-1/N*Sum[Ri])^2 The sum is from i=1 to i=N.

- #2

Science Advisor

Homework Helper

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What is "Ri"?

- #3

Homework Helper

MHB

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Hi jaobyccdee!

1/N*Sum[Ri] is the average [itex]\bar R[/itex] of [itex]R_i[/itex].

So you're asking about [itex]{1 \over N}\sum (R_i - \bar R)^2[/itex]

Does that look familiar to you?

- #4

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er...actually that's what i start with...but i don't know that it should be familiar...

- #5

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MHB

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The average of the deviation squared is called "variance".

Its square root is called "standard deviation".

- #6

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Sorry, i should have mentioned that the question starts with sqrt<R^2>, and asks to prove that it is equal to sqrt(Lζ/3). This is the relationship between contour length and the radius of gyration. So i was trying to evaluate it to something that looks like sqrt(Na/6) where Na^2 is the variance.

- #7

Homework Helper

MHB

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I can't make chocolate of all these symbols you just introduced here...

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