What kind of formula is this and how is it to be retraced?

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The discussion centers on the mathematical principles behind random walk equations, specifically addressing the term "+-2*xi(n-1)*delta" and its cancellation in the context of average displacement. Participants confirm that the term cancels out due to the symmetry of positive and negative displacements, leading to an average of zero. The analogy to the formula (a+b)(a-b) is also explored, highlighting the cancellation of inner terms. Overall, the conversation clarifies the mechanics of random walk processes and their implications in mathematical modeling.

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SansaStark
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This is basic maths but I kind of forgot how to retrace such an equation.
My question is: why does "+-2*xi(n-1)*delta" which is in the middle of the first long equation cancle out? I'm thankful for an answer!
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The context is missing, but I'll guess that this is random walk?
For a random walk process, what do you think is the average displacement?
Another way to look at it would be to consider the \pm signs - how many particles do you think will move in the + direction and how many in the - direction?
 
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Yeah, it is the random walk! :)
Do you mean that the middle part equals zero (all negatives and positive deltas are on average 0) and that's why it can be canceled out?
I thought it was some formula like (a+b)(a-b) where it's a²-ab+ab-b² where the inner parts just cancels out each other.
 

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