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need help computing covariant derivative

Started by soconne Dec 9, 2005 at 2:02 PM 1 replies 400+ views
Original Post
soconne
soconne
I understand essentially what the covariant derivative is and how it works, I'm just having a hard time solving for it. I read the following example in a text boox. Given a vector field w = sinz*e1 + cosz*e2 + (x^2 + y^2)*e3 and a vector v = 3*e1 -2*e2 + e3, find the coviariant derivative of w in the direction of v. Hence find ^vW, where the ^ is the upside down triangle. Anyway, the book said that the covariant derivative was cosz*e1 - sinz*e2 + (6x-4y)*e3. I do not understand how you get this answer. Can anyone help ?
Author Freeworld3Dhttp://www.freeworld3d.org
Eric Lengyel
Eric Lengyel
This looks like just a plain ol' directional derivative to me, not a covariant derivative. The answer you're looking for is obtained as follows.

grad w dot v = dw/dx * v.x + dw/dy * v.y + dw/dz * v.z

dw/dx = 2x * e3
dw/dy = 2y * e3
dw/dz = cos z * e1 - sin z * e2

dw/dx * v.x = 6x * e3
dw/dy * v.y = -4y * e3
dw/dz * v.z = cos z * e1 - sin z * e2

grad w dot v = (6x - 4y) * e3 + cos z * e1 - sin z * e2

soconne
soconne
Awsome, thanks.
Author Freeworld3Dhttp://www.freeworld3d.org

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