Compute quantiles (inverse distribution values) for the chi-squared distribution. using Johnson,Kotz,.. ............TODO.......
qchisqKG    (p, df, lower.tail = TRUE, log.p = FALSE)
qchisqWH    (p, df, lower.tail = TRUE, log.p = FALSE)
qchisqAppr  (p, df, lower.tail = TRUE, log.p = FALSE, tol = 5e-7)
qchisqAppr.R(p, df, lower.tail = TRUE, log.p = FALSE, tol = 5e-07,
             maxit = 1000, verbose = getOption("verbose"), kind = NULL)vector of probabilities.
degrees of freedom \(> 0\), maybe non-integer; must have length 1.
logical, see, e.g., qchisq(); must
  have length 1.
non-negative number, the convergence tolerance
the maximal number of iterations
logical indicating if the algorithm should produce “monitoring” information.
the kind of approximation; if NULL, the
    default, the approximation chosen depends on the arguments; notably it
    is chosen separately for each p.  Otherwise, it must be a
    character string.  The main approximations are
    Wilson-Hilferty versions, when the string contains "WH".
    More specifically, it must be one of the strings
particularly useful for small chi-squared values p;... ...
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particularly useful for small degrees of freedom df... ...
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qchisq.   Further, our approximations to the
  non-central chi-squared quantiles, qnchisqAppr