The definition of “vector” in math and physics

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Discussion Overview

The discussion centers around the definition of "vector" in both mathematics and physics, exploring how these definitions may vary across different contexts and disciplines. Participants examine the implications of these definitions and the nuances involved in understanding vectors as mathematical objects and physical quantities.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes a vector in APL as an array of numbers, noting that in mathematics, a list of numbers is termed a vector, while in physics, it is defined as a directed magnitude consisting of two numbers representing magnitude and direction.
  • Another participant challenges the assertion that direction can be represented by a single number, suggesting that this is only valid in two dimensions.
  • A third participant introduces the concept of vectors in linear algebra, explaining that vectors can be treated as one-dimensional arrays of numbers and are defined by their relationship to a basis in a vector space.
  • Further discussion highlights that the definition of "vector" can vary across educational stages and fields, emphasizing that not all physical quantities treated as vectors necessarily have both magnitude and direction.
  • One participant points out that while an ordered list of numbers is one example of a vector, it is not the sole definition, and the understanding of vectors must consider broader mathematical structures and axioms.

Areas of Agreement / Disagreement

Participants express differing views on the definition of vectors, particularly regarding the representation of direction and the relationship between mathematical and physical interpretations. There is no consensus on a singular definition, indicating ongoing debate and exploration of the topic.

Contextual Notes

The discussion reveals limitations in the definitions provided, including assumptions about dimensionality and the scope of what constitutes a vector in different contexts. The varying definitions across disciplines and educational levels contribute to the complexity of the discussion.

Zeynel
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I'm learning APL and this is how a vector is defined https://tryapl.org:

All data resides in arrays. An array is a rectangular collection of numbers, characters and arrays, arranged along zero or more axes. We can use more specific terms for some arrays, like a single number is a scalar, a list is a vector, and 2D arrays are matrices. Vectors can be formed by just placing elements next to each other:​

I see that in math a list of numbers is called a vector.

In physics a vector is a directed magnitude. So vector in physics is a set of only two numbers. One of these numbers is interpreted as magnitude and the other is interpreted as direction.

My question is: Is the above description correct?
 
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Zeynel said:
So vector in physics is a set of only two numbers. One of these numbers is interpreted as magnitude and the other is interpreted as direction.
This is not a correct conclusion. Direction cannot be described by a single number (unless you are just looking at two dimensions).
 
Vectors are more formally treated in a discipline known as "linear algebra". It turns out that the ability to treat a vector as a one dimensional array of numbers can then be traced to being able to identify a "basis" for a vector space. Individual vectors within the space can then be identified with unique linear combinations of basis vectors and the linear combination can [sometimes] be described as a one dimensional array of numbers.

https://en.wikipedia.org/wiki/Vector_space
 
Zeynel said:
In physics a vector is a directed magnitude.

At various stages of our education, we learn different definitions for the same word. Different definitions for the same word are used in different fields of study. So you can expect to hear different definitions of the word "vector".

As @jbriggs444 indicates, from an advanced point of view, a vector is an element of a mathematical structure that satisfies certain axioms. An ordered list of numbers is one example of a vector but an ordered list of numbers is not the only example of a vector. When you say "A vector is... such-and-such", you must think about whether your are saying a vector is identical to something or whether it is merely one example of something.

Not all physical quantities that can be treated as vectors have a "magnitude and direction". Those that do have a magnitude and direction can usually be regarded as vectors.
 
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