- #1
HJ Farnsworth
- 128
- 1
Greetings,
I have just started studying manifolds, and have come across the idea that the basis vectors can be expressed as:
e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex].
I tried to convince myself of this in 2D Cartesian coordinates using a pretty non-rigorous derivation (the idea being to get a simple intuitive grasp rather than an abstract mathematical one) starting with the position vector, as follows:
r(x,y) = xe1 + ye2
dr = [itex]\partial[/itex]r/[itex]\partial[/itex]x dx + [itex]\partial[/itex]r/[itex]\partial[/itex]y dy = [itex]\partial[/itex](xe1+ye2)/[itex]\partial[/itex]x dx + [itex]\partial[/itex](xe1+ye2)/[itex]\partial[/itex]y dy
Expand with the product rule, everything other than [itex]\partial[/itex]x/[itex]\partial[/itex]x e1dx and [itex]\partial[/itex]y/[itex]\partial[/itex]y e2dy (each partial combination is obviously 1) goes to 0 since the Cartesian basis vectors are constant and dx and dy are independent, so that:
dr = [itex]\partial[/itex]r/[itex]\partial[/itex]x dx + [itex]\partial[/itex]r/[itex]\partial[/itex]y dy = e1dx + e2dy
My first question: I would conclude that e[itex]\mu[/itex] = [itex]\partial[/itex]r/[itex]\partial[/itex]x[itex]\mu[/itex], rather than e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex]. What did I miss here?
My second question: Is there an equivalent expression to e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex] for basis one-forms? If so, could anyone please provide a quasi-derivation similar to mine above, except correct in the way mine was wrong?
Thanks for any help you can give.
-HJ Farnsworth
I have just started studying manifolds, and have come across the idea that the basis vectors can be expressed as:
e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex].
I tried to convince myself of this in 2D Cartesian coordinates using a pretty non-rigorous derivation (the idea being to get a simple intuitive grasp rather than an abstract mathematical one) starting with the position vector, as follows:
r(x,y) = xe1 + ye2
dr = [itex]\partial[/itex]r/[itex]\partial[/itex]x dx + [itex]\partial[/itex]r/[itex]\partial[/itex]y dy = [itex]\partial[/itex](xe1+ye2)/[itex]\partial[/itex]x dx + [itex]\partial[/itex](xe1+ye2)/[itex]\partial[/itex]y dy
Expand with the product rule, everything other than [itex]\partial[/itex]x/[itex]\partial[/itex]x e1dx and [itex]\partial[/itex]y/[itex]\partial[/itex]y e2dy (each partial combination is obviously 1) goes to 0 since the Cartesian basis vectors are constant and dx and dy are independent, so that:
dr = [itex]\partial[/itex]r/[itex]\partial[/itex]x dx + [itex]\partial[/itex]r/[itex]\partial[/itex]y dy = e1dx + e2dy
My first question: I would conclude that e[itex]\mu[/itex] = [itex]\partial[/itex]r/[itex]\partial[/itex]x[itex]\mu[/itex], rather than e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex]. What did I miss here?
My second question: Is there an equivalent expression to e[itex]\mu[/itex] = [itex]\partial[/itex]/[itex]\partial[/itex]x[itex]\mu[/itex] for basis one-forms? If so, could anyone please provide a quasi-derivation similar to mine above, except correct in the way mine was wrong?
Thanks for any help you can give.
-HJ Farnsworth