Differential Geometry. Honours 1996

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Discussion Overview

The discussion revolves around the notation and concepts presented in a differential geometry document, specifically focusing on the interpretation of a particular notation involving a mapping from a variable \( t \) to a function \( f(x+tv) \). The scope includes theoretical aspects of differential geometry and the clarity of mathematical notation.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the meaning of the notation \( t \mapsto f(x+tv) \), expressing confusion over the role of \( t \) and the arrow in the context of differentiation.
  • Another participant explains that the notation indicates a function mapping \( t \) to \( f(x+tv) \), noting that this is standard notation and clarifying that \( f(x+tv) \) itself is not a function but rather a value in the range of \( f \).
  • The same participant suggests that emphasizing the mapping may be unnecessary, proposing that simply using the derivative operator \( \frac{d}{dt} \) would suffice to indicate the function being differentiated.
  • A later reply acknowledges the explanation and clarifies that the notation used in the notes is \( t \mapsto f(x+tv) \) rather than \( f: \mathbb{R} \rightarrow \mathbb{R} \), indicating a specific mapping context.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding the notation, with some finding it standard while others struggle with its interpretation. No consensus is reached on the necessity of the notation's emphasis.

Contextual Notes

Participants highlight potential confusion arising from the notation and its presentation, indicating that the clarity of mathematical expressions can vary based on individual familiarity with conventions.

malawi_glenn
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http://www.maths.adelaide.edu.au/michael.murray/dg_hons/

Contents
Co-ordinate independent calculus.
Introduction
Smooth functions
Derivatives as linear operators.
The chain rule.
Diffeomorphisms and the inverse function theorem.
Differentiable manifolds
Co-ordinate charts
Linear manifolds.
Topology of a manifold
Smooth functions on a manifold.
The tangent space.
The derivative of a function.
Co-ordinate tangent vectors and one-forms.
How to calculate.
Submanifolds
Tangent space to a submanifold
Smooth functions between manifolds
The tangent to a smooth map.
Submanifolds again.
Vector fields.
The Lie bracket.
Differential forms.
The exterior algebra of a vector space.
Differential forms and the exterior derivative.
Pulling back differential forms
Integration of differential forms
Orientation.
Integration again
Stokes theorem.
Manifolds with boundary.
Stokes theorem.
Partitions of unity.
Vector fields and the tangent bundle.
Vector fields and derivations.
Tensor products
About this document ...
 
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On page 2 of the pdf, section 1.3, what does that funny arrow pointing t to f(x+tv) mean?

I just ignored the t and the arrow and only had f(x+tv) to be differentiated and it makes sense, but I still can't figure out what the t and the arrow mean.

The linear map is v to the derivative so if the arrow means some sort of mapping I don't get it as t is not mapped, v is.
 
The arrow, together with the symbols on the left and on the right, mean "the function that takes the thing on the left to the thing on the right". That part of his notation is totally standard, so I'm surprised you don't recognize it. For example, x\mapsto f(x) is the function that takes x to f(x). That function is of course usually written as f. This guy is writing t\mapsto f(x+tv)[/itex] to emphasize that that&#039;s the function he&#039;s taking the derivative of. Note that f(x+tv) isn&#039;t a function. It&#039;s a member of the range of f.<br /> <br /> In this case, it&#039;s completely pointless to emphasize that, since writing the derivative operator as d/dt is enough to show the reader what function he&#039;s taking the derivative of. It would have made more sense if he had written (t\mapsto f(x+tv))&amp;#039;(0).
 
Got it, thanks. I think the bar at the end of the arrow threw me off. The notes have

f: R --->R and not f: R |--->R

but when you insert something more specific it's:

t |---> f(x+tv)
 

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