TENSOR ANALYSIS 175
RELATIVE AND ABSOLUTE TENSORS. A tensor
Ap1... p'n
r1...rn is called a relative tensor of weight w
if its components transform according to the equation
Ag1...gl _ ax w Ap1.., pm azg1 azq i i axrn ... pix
axs1
...
axs1... sn ax r1... rn axp1 .sn
ax
where J =
2z I
is the Jacobian of the transformation. If w=0 the tensor is called absolute and is
the type of tensor with which we have been dealing above. If w= 1 the relative tensor is called a
tensor density. The operations of addition, multiplication, etc., of relative tensors are similar to
those of absolute tensors. See for example Problem 64.
SOLVED PROBLEMS
SUMMATION CONVENTION.
1. Write each of the following using the summation convention.
4 1 (a) dW = ax + '30
axe
dx2 + +
a0
dxN .
axN
(b)
dz k = a3F k dx1 + ax k dx2 + ... + ax k dxN
dt -ax1 dt ax2 dt ax' dt
(c) (x1)2 + (x2)2 + (x3)2 + ... + (xN)2.
(d) ds 2 = g11(dx1)2 + g., (dx2)2 + gas (dx3)2 .
3 3
(e) }r g dxp dxq
p=1 q=1 p9
2. Write the terms in each of the following indicated sums.
N
(a) a , xk . }; a. xk = a x1 + a x2 + ... + ajN xN jk b=, jk
= (b) Apq Aqr. Apq Aqr
q=1
Ap1A1r + Ap2A2r + ...
d% = a0 dxq
dz k _ ax k dxy'
dt axrn dt
xk xk
ds2 = gkk dxk dxk , N=3
g pq dxp dxq, N= 3
+ ApNANr
(c)