How to express vector in sigma notation

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Discussion Overview

The discussion revolves around expressing vectors in sigma notation, specifically transitioning from Cartesian coordinates to polar form. Participants explore the representation of vectors using basis vectors and the implications of dimensionality in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that a vector A can be expressed in sigma notation as ∑ Ai, where i runs from 1 to 3, corresponding to the x, y, and z coordinates.
  • Another participant corrects this to ∑ Aiei, indicating that {ei} are basis vectors, and mentions the need for basis vectors er, eθ, and eφ for polar form.
  • There is a question about the dimensionality of the angles θ and φ, with a participant expressing uncertainty about their role as components of a vector.
  • Further clarification is provided that er, eθ, and eφ are unit vectors with magnitude one, and that the components a, b, and c in the expression A = aer + beθ + ceφ are independent of the coordinates (r, θ, φ).
  • One participant notes the difficulty in finding a diagram to illustrate these concepts, suggesting a visual aid would enhance understanding.

Areas of Agreement / Disagreement

Participants express differing views on the dimensionality of the angles used in polar coordinates and how they relate to vector components. The discussion remains unresolved regarding the clarity of these concepts.

Contextual Notes

There is an indication that the definitions and roles of basis vectors in different coordinate systems may not be universally understood among participants, leading to confusion about their dimensional properties.

Who May Find This Useful

This discussion may be useful for individuals interested in vector mathematics, particularly those exploring the transition between Cartesian and polar coordinate systems in physics or engineering contexts.

reckon
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A vector A, can be expressed in sigma notation as
[tex]\sum[/tex] Ai where i runs from 1 to 3, i.e. A1 for x coordinate, A2 for y coordinate and A3 for z coordinate.

I wonder how to express vector A in polar form using sigma notation. Could anyone share their knowledge to me?
 
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Welcome to PF!

Hi reckon ! Welcome to PF! :smile:

(have a sigma: ∑ :wink:)
reckon said:
A vector A, can be expressed in sigma notation as
[tex]\sum[/tex] Ai where i runs from 1 to 3, i.e. A1 for x coordinate, A2 for y coordinate and A3 for z coordinate.

No, it's ∑ Aiei, where the {ei} are basis vectors.
I wonder how to express vector A in polar form using sigma notation. Could anyone share their knowledge to me?

You'd need to use the basis vectors er eθ and eφ.

But these are different at each point, and at the origin they aren't even defined.
 
Hahaha.. thanks tiny-tim for ∑ and you even provided with "for copying-pasting" in your signature.

But I'm still a bit unsure because for eθ eφ, we only have angle which doesn't have dimension, isn't it? Can we make them as component of a vector?

A=rer + θeθ + φeφ
where r have length dimension while θ and φ have no dimension?
 
Hi reckon! :smile:
reckon said:
But I'm still a bit unsure because for eθ eφ, we only have angle which doesn't have dimension, isn't it? Can we make them as component of a vector?

A=rer + θeθ + φeφ
where r have length dimension while θ and φ have no dimension?

ah … you obviously haven't come across these before …

no, er eθ and eφ are all unit vectors (with magnitude one), in the directions of increasing r, increasing θ, and increasing φ, respectively …

so they all have length dimension.

(it is traditional to use the symbol e for unit vectors)

A vector starting at the position (r,θ,φ) will be written as aer + beθ + ceφ, and a b and c have nothing to do with (r,θ,φ), they are simply the components of the vector in each of the three (perpendicular) directions. :smile:

(this would be easier to follow with a diagram, but unfortunately, I can't find a good one, in wikipedia or anywhere else :redface:)
 

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