Quantile-quantile plot

`qqplot(X)`

qqplot(X,Y)

qqplot(X,PD)

qqplot(X,Y,pvec)

h = qqplot(X,Y,pvec)

`qqplot(X)`

displays a quantile-quantile
plot of the sample quantiles of `X`

versus theoretical
quantiles from a normal distribution. If the distribution of `X`

is
normal, the plot will be close to linear.

`qqplot(X,Y)`

displays a quantile-quantile
plot of two samples. If the samples do come from the same distribution,
the plot will be linear.

`qqplot(X,PD)`

makes an empirical
quantile-quantile plot of the quantiles of the data in the vector `X`

versus
the quantiles of the distribution specified by `PD`

,
a `ProbDist`

object of the `ProbDistUnivParam`

class or `ProbDistUnivKernel`

class.

For matrix `X`

and `Y`

, `qqplot`

displays
a separate line for each pair of columns. The plotted quantiles are
the quantiles of the smaller data set.

The plot has the sample data displayed with the plot symbol `'+'`

.
Superimposed on the plot is a line joining the first and third quartiles
of each distribution (this is a robust linear fit of the order statistics
of the two samples). This line is extrapolated out to the ends of the sample to help evaluate
the linearity of the data.

Use `qqplot(X,Y,pvec)`

to specify the quantiles
in the vector `pvec`

.

`h = qqplot(X,Y,pvec)`

returns
handles to the lines in `h`

.

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