popdemo (version 1.3-1)

convt: Calculate time to convergence

Description

Calculate the time to convergence of a population matrix projection model from the model projection

Usage

convt(A, vector = "n", accuracy = 0.01, iterations = 1e+05)

Arguments

A

a square, non-negative numeric matrix of any dimension

vector

(optional) a numeric vector or one-column matrix describing the age/stage distribution used to calculate the projection.

accuracy

the accuracy with which to determine convergence on asymptotic growth, expressed as a proportion (see details).

iterations

the maximum number of iterations of the model before the code breaks. For slowly-converging models and/or high specified convergence accuracy, this may need to be increased.

Value

If vector is specified, the convergence time of vector projected through A.

If vector is not specified, a numeric vector of convergence times for corresponding stage-biased projections: the length of the vector is equal to the dimension of A; the first entry is the convergence time of [1,0,0,...], the second entry is the convergence time of [0,1,0,...], etc.).

Details

convt works by simulating the given model and manually determining growth when convergence to the given accuracy is reached. Convergence on an asymptotic growth is deemed to have been reached when the growth of the model stays within the window determined by accuracy for 10*s iterations of the model, with s equal to the dimension of A. For example, projection of an 8 by 8 matrix with convergence accuracy of 1e-2 is deemed to have converged on asymptotic growth when 10*8=80 consecutive iterations of the model have a growth within 1-1e-2=0.99 (i.e. 99%) and 1+1e-2=1.01 (i.e. 101%) of each other.

If vector is specified, the convergence time of the projection of vector through A is returned. If vector="n" then asymptotic growths of the set of 'stage-biased' vectors are calculated. These projections are achieved using a set of standard basis vectors equal in number to the dimension of A. These have every element equal to 0, except for a single element equal to 1, i.e. for a matrix of dimension 3, the set of stage-biased vectors are: c(1,0,0), c(0,1,0) and c(0,0,1).

Due to the way in which convergence is defined, convt can only properly work for strongly ergodic models. Therefore, it will not function for imprimitive (therefore potentially weakly ergodic) or reducible (therefore potentially nonergodic) models.

References

• Stott et al. (2011) Ecol. Lett., 14, 959-970.

See Also

Other ConvergenceMeasures: dr(), truelambda()

Examples

# NOT RUN {
 # Create a 3x3 PPM
 ( A <- matrix(c(0,1,2,0.5,0.1,0,0,0.6,0.6), byrow=TRUE, ncol=3) )

 # Create an initial stage structure
 ( initial <- c(1,3,2) )

 # Calculate the convergence time of the 3 stage-biased 
 # populations within 0.1% of lambda-max
 ( convt(A, accuracy=1e-3) )

 # Calculate the convergence time of the projection of initial and A
 # to within 0.001% of lambda-max
 ( convt(A, vector=initial, accuracy=1e-5) )

# }