pairs.stanfit {rstan} | R Documentation

## Create a matrix of output plots from a `stanfit` object

### Description

A `pairs` method that is customized for MCMC output

### Usage

      ## S3 method for class 'stanfit'
    pairs(x, labels = NULL, panel = NULL, ...,
        lower.panel = NULL,
        upper.panel = NULL, diag.panel = NULL, text.panel = NULL,
        label.pos = 0.5 + 1/3, cex.labels = NULL, font.labels = 1,
        row1attop = TRUE, gap = 1, log = "", pars = NULL, condition = "accept_stat__",
        include = TRUE)

### Arguments

`x` | An object of S4 class `stanfit`
`labels, panel, ..., lower.panel, upper.panel, diag.panel` | Same as in `pairs` syntactically but see the Details section for different default arguments
`text.panel, label.pos, cex.labels, font.labels, row1attop, gap` | Same as in `pairs.default`
`log` | Same as in `pairs.default`, which makes it possible to utilize logarithmic axes and additionally accepts `log = TRUE`. See the Details section.
`pars` | If not `NULL`, a character vector indicating which quantities to include in the plots, which is passed to `extract`. Thus, by default, all unknown quantities are included, which may be far too many to visualize on a small computer screen. If `include = FALSE`, then the named parameters are excluded from the plot.

`condition`

If `NULL`, it will plot roughly half of the chains in the lower panel and the rest in the upper panel. An integer vector can be passed to select some subset of the chains, of which roughly half will be plotted in the lower panel and the rest in the upper panel. A list of two integer vectors can be passed, each specifying a subset of the chains to be plotted in the lower and upper panels respectively.

A single number between zero and one exclusive can be passed, which is interpreted as the proportion of realizations (among all chains) to plot in the lower panel starting with the first realization in each chain, with the complement (from the end of each chain) plotted in the upper panel.

A (possibly abbreviated) character vector of length one can be passed among `"accept_stat__", "stepsize__"`, `"treedepth__", "n_leapfrog__"`, `"divergent__"`,, `"energy__"`, or `"lp__"`, which are the variables produced by `get_sampler_params` and `get_logposterior`. In that case the lower panel will plot realizations that are below the median of the indicated variable (or are zero in the case of `"divergent__"`) and the upper panel will plot realizations that are greater than or equal to the median of the indicated variable (or are one in the case of `"divergent__"`). Finally, any logical vector whose length is equal to the product of the number of iterations and the number of chains can be passed, in which case realizations corresponding to `FALSE` and `TRUE` will be plotted in the lower and upper panel respectively. The default is `"accept_stat__"`.

`include` | Logical scalar indicating whether to include (the default) or excldue the parameters named in the `pars` argument from the plot.

### Details

This method differs from the default `pairs` method in the following ways. If unspecified, the `smoothScatter` function is used for the off-diagonal plots, rather than `points`, since the former is more appropriate for visualizing thousands of draws from a posterior distribution. Also, if unspecified, histograms of the marginal distribution of each quantity are placed on the diagonal of the plot, after pooling all of the chains specified by the `chain\_id` argument.

The draws from the warmup phase are always discarded before plotting.

By default, the lower (upper) triangle of the plot contains draws with below (above) median acceptance probability. Also, if `condition` is not `"divergent__"`, red points will be superimposed onto the smoothed density plots indicating which (if any) iterations encountered a divergent transition. Otherwise, yellow points indicate a transition that hit the maximum treedepth rather than terminated its evolution normally.

You may very well want to specify the `log` argument for non-negative parameters. However, the `pairs` function will drop (with a message) parameters that are either constant or duplicative with previous parameters. For example, if a correlation matrix is included among `pars`, then neither its diagonal elements (which are always 1) nor its upper triangular elements (which are the same as the corresponding lower triangular elements) will be included. Thus, if `log` is an integer vector, it needs to pertain to the parameters after constant and duplicative ones are dropped. It is perhaps easiest to specify `log = TRUE`, which will utilize logarithmic axes for all non-negative parameters, except `lp__` and any integer valued quantities.

### See Also

S4 class `stanfit` and its method `extract` as well as the `pairs` generic function. Also, see `get_sampler_params` and `get_logposterior`.

### Examples

    example(read_stan_csv)
    pairs(fit, pars = c("mu", "sigma", "alpha", "lp__"), log = TRUE, las = 1)
    # sigma and alpha will have logarithmic axes

[Package rstan version 2.16.2 Index]