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

[jaobyccdee]

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

 

[HallsofIvy]

What is "Ri"?

 

[I like Serena]

Hi jaobyccdee!


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

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

Does that look familiar to you?

 

[jaobyccdee]

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

 

[I like Serena]

The average of the deviation squared is called "variance".
Its square root is called "standard deviation".

 

[jaobyccdee]

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.

 

[I like Serena]

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.

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