CKAVG     CKAVG     CKAVG     CKAVG     CKAVG     CKAVG     CKAVG     
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SUBROUTINE CKAVG (NN, S1, S2, SAVG)
For arrays of length nn,
SAVG(n) is the average value of S1(n) and S2(n).

INPUT
NN    - The length of the two input arrays.
S1    - Real array.
S2    - Real array.

OUTPUT
SAVG  - Real array, sum of S1 and S2
SAVG(n) is the average value of S1(n) and S2(n).