R: Phase portrait plot

phasePortrait {phaseR}

R Documentation

Phase portrait plot

Description

For a one-dimensional autonomous ODE, it plots the phase portrait, i.e., the derivative against the dependent variable. In addition, along the dependent variable axis it plots arrows pointing in the direction of dependent variable change with increasing value of the independent variable. From this stability of equilibrium points (i.e., locations where the horizontal axis is crossed) can be determined.

Usage

phasePortrait(
  deriv,
  ylim,
  ystep = 0.01,
  parameters = NULL,
  points = 10,
  frac = 0.75,
  arrow.head = 0.075,
  col = "black",
  add.grid = TRUE,
  state.names = "y",
  xlab = state.names,
  ylab = paste0("d", state.names),
  ...
)

Arguments

`deriv`	A function computing the derivative at a point for the ODE system to be analysed. Discussion of the required structure of these functions can be found in the package vignette, or in the help file for the function `ode`.
`ylim`	Sets the limits of the dependent variable for which the derivative should be computed and plotted. Should be a `numeric` `vector` of `length` two.
`ystep`	Sets the step length of the dependent variable vector for which derivatives are computed and plotted. Decreasing `ystep` makes the resulting plot more accurate, but comes at a small cost to computation time. Defaults to `0.01`.
`parameters`	Parameters of the ODE system, to be passed to `deriv`. Supplied as a `numeric` `vector`; the order of the parameters can be found from the `deriv` file. Defaults to `NULL`.
`points`	Sets the density at which arrows are plotted along the horizontal axis; `points` arrows will be plotted. Fine tuning here, by shifting `points` up and down, allows for the creation of more aesthetically pleasing plots. Defaults to `10`.
`frac`	Sets the fraction of the theoretical maximum length line segments can take without overlapping, that they actually attain. Fine tuning here assists the creation of aesthetically pleasing plots. Defaults to `0.75`.
`arrow.head`	Sets the length of the arrow heads. Passed to `arrows`. Defaults to `0.075`.
`col`	Sets the colour of the line in the plot, as well as the arrows. Should be a `character` `vector` of `length` one. Will be reset accordingly if it is of the wrong `length`. Defaults to `"black"`.
`add.grid`	Logical. If `TRUE`, a grid is added to the plot. Defaults to `TRUE`.
`state.names`	The state names for `ode` functions that do not use positional states.
`xlab`	Label for the x-axis of the resulting plot.
`ylab`	Label for the y-axis of the resulting plot.
`...`	Additional arguments to be passed to either plot or arrows.

Value

Returns a list with the following components:

`add.grid`	As per input.
`arrow.head`	As per input.
`col`	As per input, but with possible editing if a `character` `vector` of the wrong `length` was supplied.
`deriv`	As per input.
`dy`	A `numeric` `vector` containing the value of the derivative at each evaluated point.
`frac`	As per input.
`parameters`	As per input.
`points`	As per input.
`xlab`	As per input.
`y`	A `numeric` `vector` containing the values of the dependent variable for which the derivative was evaluated.
`ylab`	As per input.
`ylim`	As per input.
`ystep`	As per input.

Author(s)

Michael J Grayling

Examples

# A one-dimensional autonomous ODE system, example2.
example2_phasePortrait <- phasePortrait(example2,
                                        ylim   = c(-0.5, 2.5),
                                        points = 10,
                                        frac   = 0.5)

[Package phaseR version 2.2.1 Index]