Talk:Algebra homomorphism

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Mathematics rating:	Stub Class	Mid Priority	Field: Algebra
Please update this rating as the article progresses, or if the rating is inaccurate. Click to show/hide comments. Please add to or update the comments to suggest improvements to the article. Cronholm144 01:33, 14 May 2007 (UTC)

My understanding of homomorphism leads me to believe that the first two conditions given in the first sections follow from the nature of algebras not from the nature of homomorphism and that the third condition is the rule that makes a homomorphism what it is. Input appreciated--Cronholm144 04:55, 14 May 2007 (UTC)

In general a homomorphism preserves all the structure of the underlying object. With an algebra a homomorphism must preserve addition and multiplication (the two binary operations of the underlying set) and scalar multiplication. Contrast this to a group which only needs preserve multiplication to be a homomorphism (technically you need the identity to map to the identity and inverse to map to inverses, but this all follows from the homomorphism respecting multiplcation). TooMuchMath 05:20, 15 May 2007 (UTC)

got it, thanks... sorry for sending you down a false trail--Cronholm144 05:41, 15 May 2007 (UTC)

Injectivity of a k-algebra homomorphism isn't enough for an isomorphism. Let k be a field and K an extension field such that . Then viewing k and K as k-algebras, the inclusion is an injective k-algebra homomorphism which isn't an isomorphism. Steve Checkoway 04:55, 12 November 2007 (UTC)

This is clear, and your edit definitely corrected a mistake. Had they left out injectivity and required surjectivity, I would assume they were talking about simple algebras. At any rate, since they weren't mentioned in the article, I linked them in with a discussion of inner automorphisms. JackSchmidt 05:06, 12 November 2007 (UTC)