FIG. 1.

Identifying the boundary limit. For the exponential model in the text with eight parameters, initially, the least sensitive parameter combination involves many parameters and is difficult to remove (inset, top left). By following a geodesic to the manifold boundary (solid line), the combination rotates to reveal a limiting behavior; here, only one parameter (an exponential rate) becomes zero (inset, bottom left). As the boundary is approached, one eigenvalue of the FIM approaches zero (inset, right). Once the smallest eigenvalue becomes well separated from the other eigenvalues, the limiting behavior becomes apparent. This limit is largely independent of the starting point; nearby parameter values all map to the same simplified model (dashed lines).