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Metric spaces and open sets
Distance made abstract; open balls, open and closed sets, continuity.
A metric is any distance obeying symmetry, positivity and the triangle inequality. Open sets are unions of open balls; a function is continuous when preimages of open sets are open. No ε needed once the open sets are known. Picture it: the open disc around a point, and the same idea with the "taxicab" distance making diamonds. Think it: topology keeps the open sets and throws the metric away.
Ohatra · distance between (1,2) and (4,6)
Dingana amin'ny dingana
- \Delta x = 3,\ \Delta y = 4
Differences of the coordinates.
- d = \sqrt{\Delta x^2 + \Delta y^2} = \sqrt{9 + 16} = 5
Distance formula (Pythagoras).
Asehoy ny valinteny
Ankehitriny ianao Misafidiana olana iray, na soraty na esory ny anao manokana. Ny dingana tsirairay, sary iray, ny valiny miafina mandra-pahafantaranao.
Ny kaonty maimaimpoana dia mampiditra ny fanamarihana amin'ny lesona tsirairay, ny tahirin'ny zavatra vitanao, ny olana voavahao ao amin'ny toerana iray, ary ny mpampianatra iray izay azonao anontanio momba ity pejy ity. misokatra ho an'ny rehetra ny matematika, na efa niditra na tsy niditra.
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Ahoana ny fomba: Metric spaces and open sets
- Differences of the coordinates.
- Distance formula (Pythagoras).
Fanontaniana napetrak'ireo olona
Why "a doughnut is a coffee cup"?
Each can be deformed into the other without cutting or gluing: one hole each. Topology studies exactly the properties such deformations preserve.
What is compactness for?
It is the property that makes "every sequence has a convergent subsequence" and "continuous functions attain their maximum" true. On the real line it means closed and bounded.
Mbola maro ao Topology
Compactness and connectednessHomeomorphism and topological invariants