Differentiation
. The element of arc of 'Y at p is given by
ds^2 = dx · dx = L(dxi)^2
i
399
the dxi being direction numbers of the tangent line to -y* at p. The
corresponding element of arc of r at f(p) is given by
da^2 = dy · dy = L(dyi)^2 = Mjkdxidxk
i
j' k = 1, ... ' n, the dyi being direction numbers of the tangent line to r*
at f(p), and
Hence the square of the magnification ratio p = da / ds is given by
2 Mjkdxidxk
p = I:;( dxi)2
This ratio is independent of the direction numbers dxi iff
for j =/:-k and
M denoting a positive constant at p. Then we have
p2 =M
(6.24-17)
(6~24-18)
With the notation aii = ofi/oxi, and using (6.24-18), equations (6.24-
- can be written as
(a11)2 + ... + (an1)2 = ... = (aln)2 + .. , + (ann)2 = P2
ana12 + .. , + anlan2 = O
alla13 + ... + anlan3 = O
Consider the n equations containing a^1 i , ... ,ani, namely,
allalj + a21a2j + ... + anlanj = O
alj alj + a2i a2j + .. , + anj anj = P2