CKBSEC    CKBSEC    CKBSEC    CKBSEC    CKBSEC    CKBSEC    CKBSEC    
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REAL FUNCTION CKBSEC (NPTS, X, XX, TT)
Interpolate f(X) using bisection, given X and other pairs
of X and f(X).

INPUT
NPTS	  - Integer scalar, total pairs of data.
X      - Real scalar, location for which f(X) is required.
XX(*)  - Real array, locations for which data is given.
TT(*)  - Real array, function values for locations given.