flowField: Flowfield In epimdr: Functions and Data for "Epidemics: Models and Data in R"

Description

Plots the flow or velocity field for a one- or two-dimensional autonomous ODE system.

Usage

 1 2 3 4 5 flowField(deriv, xlim, ylim, parameters = NULL, system = "two.dim", points = 21, col = "gray", arrow.type = "equal", arrow.head = 0.05, frac = 1, add = TRUE, xlab = if (system == "two.dim") state.names else "t", ylab = if (system == "two.dim") state.names else state.names, ...)

Arguments

 deriv A function computing the derivative at a point for the ODE system to be analysed. Discussion of the required format of these functions can be found in the package vignette, or in the help file for the function ode. xlim In the case of a two-dimensional system, this sets the limits of the first dependent variable in which gradient reflecting line segments should be plotted. In the case of a one-dimensional system, this sets the limits of the independent variable in which these line segments should be plotted. Should be a numeric vector of length two. ylim In the case of a two-dimensional system this sets the limits of the second dependent variable in which gradient reflecting line segments should be plotted. In the case of a one-dimensional system, this sets the limits of the dependent variable in which these line segments should be plotted. Should be a numeric vector of length two. 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. system Set to either "one.dim" or "two.dim" to indicate the type of system being analysed. Defaults to "two.dim". points Sets the density of the line segments to be plotted; points segments will be plotted in the x and y directions. Fine tuning here, by shifting points up and down, allows for the creation of more aesthetically pleasing plots. Defaults to 11. col Sets the colour of the plotted line segments. Should be a character vector of length one. Will be reset accordingly if it is of the wrong length. Defaults to "gray". arrow.type Sets the type of line segments plotted. If set to "proportional" the length of the line segments reflects the magnitude of the derivative. If set to "equal" the line segments take equal lengths, simply reflecting the gradient of the derivative(s). Defaults to "equal". arrow.head Sets the length of the arrow heads. Passed to arrows. Defaults to 0.05. frac Sets the fraction of the theoretical maximum length line segments can take without overlapping, that they can actually attain. In practice, frac can be set to greater than 1 without line segments overlapping. Fine tuning here assists the creation of aesthetically pleasing plots. Defaults to 1. add Logical. If TRUE, the flow field is added to an existing plot. If FALSE, a new plot is created. Defaults to TRUE. 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 (the exact make up is dependent on the value of system):

 add As per input. arrow.head As per input. arrow.type 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. dx A numeric matrix. In the case of a two-dimensional system, the values of the derivative of the first dependent derivative at all evaluated points. dy A numeric matrix. In the case of a two-dimensional system, the values of the derivative of the second dependent variable at all evaluated points. In the case of a one-dimensional system, the values of the derivative of the dependent variable at all evaluated points. frac As per input. parameters As per input. points As per input. system As per input. x A numeric vector. In the case of a two-dimensional system, the values of the first dependent variable at which the derivatives were computed. In the case of a one-dimensional system, the values of the independent variable at which the derivatives were computed. xlab As per input. xlim As per input. y A numeric vector. In the case of a two-dimensional system, the values of the second dependent variable at which the derivatives were computed. In the case of a one-dimensional system, the values of the dependent variable at which the derivatives were computed. ylab As per input. ylim As per input.

Author(s)

Michael J Grayling