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Universal properties, limits and adjunctions

Products, coproducts, limits and the adjunctions that unify constructions.

A product is defined by what maps into it, not by what it is made of; the same shape of definition gives limits, colimits and free objects. Adjoint functors pair a "free" construction with a "forgetful" one. Picture it: the lcm of 4 and 6 is the least common multiple in the divisibility order, a categorical join. Think it: Yoneda: an object is determined by the arrows into it.

Apdorotas pavyzdys · lcm(4, 6)

Lcm(4, 6)

4,\ 6

Žingsnis po žingsnio

  1. \gcd(4, 6)

    Use Euclid's algorithm: replace the larger number by its remainder on division by the smaller, until the remainder is 0.

  2. 6 = 1 \times 4 + 2

    Divide 6 by 4: quotient 1, remainder 2.

  3. 4 = 2 \times 2 + 0

    Divide 4 by 2: quotient 2, remainder 0.

  4. \gcd(4, 6) = 2

    Euclid gives the gcd.

  5. \operatorname{lcm}(4, 6) = \frac{4 \times 6}{\gcd(4, 6)} = \frac{24}{2} = 12

    lcm × gcd = a × b, so divide the product by the gcd.

Atskleisti atsakymą
\operatorname{lcm}(4, 6) = 12

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Kaip vartoti: Universal properties, limits and adjunctions

  1. Use Euclid's algorithm: replace the larger number by its remainder on division by the smaller, until the remainder is 0.
  2. Divide 6 by 4: quotient 1, remainder 2.
  3. Divide 4 by 2: quotient 2, remainder 0.
  4. Euclid gives the gcd.
  5. lcm × gcd = a × b, so divide the product by the gcd.

Klausimai, kuriuos klausia žmonės

What is a functor?

A map between categories that sends objects to objects and arrows to arrows while respecting composition. Taking the fundamental group of a space is a functor from spaces to groups.

Daugiau informacijos Category Theory