Understanding Projection: Clarifying Confusion in Orthogonal Projections

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SUMMARY

The discussion clarifies the conditions under which a projection P is classified as an orthogonal projection. Specifically, it states that if a projection satisfies the inequality || P v || <= || v ||, it must be an orthogonal projection only if the projection is performed perpendicularly to the line of projection. The confusion arises when projecting vectors onto the line y = x without ensuring perpendicularity, which can lead to incorrect interpretations of the norm inequality.

PREREQUISITES
  • Understanding of vector norms and their properties
  • Familiarity with the concept of orthogonal projections in linear algebra
  • Knowledge of geometric interpretations of vector projections
  • Basic proficiency in R² coordinate systems
NEXT STEPS
  • Study the mathematical definition of orthogonal projections in linear algebra
  • Learn how to compute projections in R² using matrix representations
  • Explore the geometric implications of non-orthogonal projections
  • Investigate the properties of vector norms in different contexts
USEFUL FOR

Students and educators in mathematics, particularly those studying linear algebra and vector calculus, as well as anyone seeking to deepen their understanding of orthogonal projections and their applications.

holezch
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Homework Statement


Hi, I got tied up with something..
I have a question that says if a projection P satisfies || P v || <= || v ||
then P is an orthogonal projection.. but if I drew in |R^2, a x-axis and a y=x line, and projected some vector onto the y = x line.. I still get || Pv || <= || V || ? I think Iam doing something wrong

thanks
 
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When you say you project V onto the y = x line, are you projecting it perpendicular to the line? I mean thinking of the tip of V projecting perpendicularly to the line? And if so, what's the problem? If you are projecting, for example, vertically to the line then you don't have your norm inequality.
 

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