niche_presence_only: Fit presence-only Gaussian niche model

In xnicher: Estimates Ecological Niche Models Using Ellipses

Fit presence-only Gaussian niche model

Description

Fits a multivariate normal niche model using only presence records, with no background correction (Jimenez et al. 2019, Eq. 2). Uses the compiled C++ backend via an external pointer for fast evaluation.

Usage

niche_presence_only(occ, eta = 1, start = NULL, ...)

Arguments

occ	Numeric matrix (n \times p) of environmental values at presence points.
eta	Numeric scalar, shape parameter for the LKJ C-vine prior on the correlation matrix (default 1 = uniform over correlations).
start	A numeric vector (single-start) or list of numeric vectors (multi-start). Use [start_theta()] or [start_theta_multiple()] to generate starting values.
...	Ignored. Present for wrapper compatibility.

Details

The minimised objective is the negative log-likelihood of the unconstrained multivariate normal:

-\log\mathcal{L} = \frac{n}{2}\log|\Sigma| + \frac{1}{2}\sum_{i=1}^{n} q_i

where q_i = (\mathbf{x}_i - \mu)^\top \Sigma^{-1} (\mathbf{x}_i - \mu).

Supports both single-start (start is a numeric vector) and multi-start (start is a list of numeric vectors) optimisation.

Value

A list with components:

theta

Best parameter vector.

value

Negative log-likelihood at the optimum.

conv

Convergence code (0 = success).

all_results

Data frame of all starts (multi-start only).

References

Jimenez, L., Soberon, J., Christen, J. A., & Soto, D. (2019). On the problem of modeling a fundamental niche from occurrence data. Ecological Modelling, 397, 109823.

See Also

[optimize_niche()] for the unified fitting interface, [loglik_niche_math_presence_only()] for the R-level log-likelihood.

Examples

occ    <- as.matrix(example_env_occ_3d)
theta0 <- start_theta(example_env_occ_3d)
res    <- niche_presence_only(occ = occ, start = theta0)
res$value

xnicher documentation built on Sept. 15, 2026, 5:08 p.m.