How to Simplify the Mean of 3D Variables to 1D?

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Discussion Overview

The discussion revolves around the simplification of the mean value of three-dimensional variables ax, ay, and az to a one-dimensional mean of the absolute value of ax. Participants explore the necessary assumptions and theoretical properties involved in this simplification process.

Discussion Character

  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant questions how to simplify the mean value <(ax^2+ay^2+az^2)^(1/2)> to <|ax|> and asks what assumptions are necessary for this simplification.
  • Another participant suggests that no further assumptions are needed for the calculation, although they note that the process is complicated due to the square root being taken before the integral is calculated.
  • A different participant expresses uncertainty about the theoretical properties that could be applied to the problem and seeks clarification.
  • It is mentioned that the problem involves a three-dimensional integral where the integrand includes the product of the three density functions along with the square root expression.
  • A participant reiterates the original question, asking if the mean value of r = \sqrt{a_x^2 + a_y^2 + a_z^2} must equal the mean value of the absolute value of a_x.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the assumptions required for the simplification or the theoretical properties applicable to the problem. Multiple viewpoints and uncertainties remain present in the discussion.

Contextual Notes

Participants highlight that the statistical property of the variables includes == and that the probability density functions are independent of each other. However, the implications of these properties on the simplification process are not fully resolved.

pangyatou
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Hi,

There are three variables ax, ay and az, my question is:
How to simplify the mean value <(ax^2+ay^2+az^2)^(1/2)> to <|ax|> ?
What assumptions are required during the simplification?

The statistical property of ax, ay and az is <ax^2>=<ay^2>=<az^2>.
The assumption of the propability is: pdf(ax), pdf(ay) and pdf(az) are independent to each other: p(ax,ay,az)=p(ax)p(ay)p(az)

Thanks
 
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No further assumptions are needed to carry out the calculation. It is messy because you are taking the square root before calculating the integral.
 
Thanks Mathman!
What theory or property can be applied to this problem? I don't even have a clue.

Really appreciate.
 
It is a 3-d integral where the integrand is the product of the 3 density functions multiplied by the expression (square root etc.).
 
pangyatou said:
Hi,

There are three variables ax, ay and az, my question is:
How to simplify the mean value <(ax^2+ay^2+az^2)^(1/2)> to <|ax|> ?
What assumptions are required during the simplification?

Are you asking if the mean value of r = \sqrt{a_x^2 + a_y^2 + a_z^2} must be equal to the mean value of the absolute value of a_x ?
 

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