Description Usage Arguments Value Details
The utility function pm_obj_func
computes the total distance between
observed predator signatures and vector of mean diet proportions common to
all predators.
1 | pm_obj_func(diet, obs_sig, mean_sigs, dist_meas = 1, gamma = 1)
|
diet |
A numeric vector of mean diet composition. |
obs_sig |
A numeric matrix containing observed predator signatures, in column-major format. |
mean_sigs |
A numeric matrix of the mean fatty acid signature for each prey type in the prey library, in column-major format. |
dist_meas |
An integer indicator of the distance measure to compute. Default value 1. |
gamma |
The power parameter of the chi-square distance measure. Default value 1. |
The total distance between observed and modeled signatures.
This is an internal utility function. Consequently, to increase execution
speed, no numeric error checking is performed within pm_obj_func
.
Rather, error checking is presumed to have occurred at a higher level in the
calling sequence.
The argument obs_sig
is presumed to be a matrix of predator
signatures that has been prepared for analysis, which is best accomplished
by a call to the function prep_sig
with the predator data.
Similarly, the contents of mean_sigs
should be mean signatures computed
from signatures that were prepared for analysis by a call to the function
prep_sig
.
The argument diet
is presumed to contain non-negative proportions that
sum to 1.0.
The arguments dist_meas
and gamma
must be compatible with the
function dist_between_2_sigs
.
Please refer to the vignette and documentation for the functions
prep_sig
, sig_scale
, and
dist_between_2_sigs
for additional details.
diet_obj_func
models a predator signature as a mixture of the mean
prey-type signatures, with the diet proportions as the mixture proportions,
returning the distance between the observed and modeled signatures. The
diet composition of a predator is estimated by minimizing this function with
respect to the diet
using the function Rsolnp::solnp.
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