On Tuesday, 10 August 2021 at 20:54:02 UTC-7 Nils Bruin wrote:
>
> V=VectorSpace(GF(2),3)
> v = V.gen(1)
> w = V.gen(2)
> v.set_immutable() #this is annoying, but OK
> w.set_immutable() #this is again annoying
> D={}
> D[v]=1
> D[w]=2
> D[v+w]=3 #the error here is uncalled for!
>
> It's actually worse than that! The stored generators of a vector space are
actually immutable! So the session really goes:
V=VectorSpace(GF(2),3)
D={}
D[V.1]=1 #happy
D[V.2]=2 #still happy
D[V.1+V.2]=3 # Error??? !@#?! Why is the sum of two vectors now suddenly
mutable??
This is a very surprising scenario. It happens in real life. I know because
it happened to me.
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