Why Are Open Domains Essential for Smooth Functions in Rn?

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SUMMARY

Open domains are essential for defining smooth functions in Rn because they ensure the presence of tangent spaces necessary for the function's graph. A function defined on a single point lacks a tangent line, while a function on a curve in the plane cannot possess a tangent plane. Smoothness implies that the graph must be sufficiently large, or "fat," to accommodate these tangent structures, which is only guaranteed in an open set.

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  • Understanding of smooth functions in mathematical analysis
  • Familiarity with vector fields in Rn
  • Knowledge of tangent spaces and their significance
  • Basic concepts of topology, specifically open sets
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jimisrv
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Hi, I have a quick question:

When we talk about smooth functions (say a vector field on Rn), why must we usually restrict the domain to an open set in Rn?

Thanks!
 
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ask yourself what it would mean to say the graph of a function defined on a one point set has a tangent line?

similarly what would it mean to say the graph of a function on a curve in the plane has a tangent plane?

smooth means there are tangent spaces to the graph, so the graph should be big enough to have a tangent plane.

so the domain has to be kind of fat, i.e. open. in order to have the right dimension.
 

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