ASKSAGE: Sage Q&A Forum - Individual question feedhttp://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Mon, 27 Aug 2018 13:51:55 -0500How do I define a homomorphism of a graded commutative algebra?http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/Why does the following throw a `TypeError: images do not define a valid homomorphism`?
E = GradedCommutativeAlgebra(QQ,'x,y',degrees=(1,1))
E.inject_variables()
f = E.hom([x,y])
I expected it to define $f$ to be the identity homomorphism of $E$. What is the right way to define a homomorphism of $E$? I'm more interested in the one that switches $x$ and $y$ than the identity homomorphism, but this seemed a more obvious version of the question.Sat, 28 Apr 2018 12:14:46 -0500http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/Comment by John Palmieri for <p>Why does the following throw a <code>TypeError: images do not define a valid homomorphism</code>?</p>
<pre><code>E = GradedCommutativeAlgebra(QQ,'x,y',degrees=(1,1))
E.inject_variables()
f = E.hom([x,y])
</code></pre>
<p>I expected it to define $f$ to be the identity homomorphism of $E$. What is the right way to define a homomorphism of $E$? I'm more interested in the one that switches $x$ and $y$ than the identity homomorphism, but this seemed a more obvious version of the question.</p>
http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/?comment=43492#post-id-43492I am working on implementing morphisms of graded commutative algebras. No promises about when it might be done, but what are you interested in doing with the morphisms? What features would you like to have?Mon, 27 Aug 2018 13:51:55 -0500http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/?comment=43492#post-id-43492Answer by John Palmieri for <p>Why does the following throw a <code>TypeError: images do not define a valid homomorphism</code>?</p>
<pre><code>E = GradedCommutativeAlgebra(QQ,'x,y',degrees=(1,1))
E.inject_variables()
f = E.hom([x,y])
</code></pre>
<p>I expected it to define $f$ to be the identity homomorphism of $E$. What is the right way to define a homomorphism of $E$? I'm more interested in the one that switches $x$ and $y$ than the identity homomorphism, but this seemed a more obvious version of the question.</p>
http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/?answer=42239#post-id-42239This looks like a bug, and I'm not sure of a workaround yet.
I created a ticket for it [here](https://trac.sagemath.org/ticket/25276).Tue, 01 May 2018 12:21:26 -0500http://ask.sagemath.org/question/42202/how-do-i-define-a-homomorphism-of-a-graded-commutative-algebra/?answer=42239#post-id-42239