biexp_start: Grid-profiled starting estimates for the biexponential model

In mnirs: Muscle Near-Infrared Spectroscopy Processing and Analysis

Grid-profiled starting estimates for the biexponential model

Description

Vector-level initialiser behind biexp_init(), called directly by the kinetics worker with tau and TD held at their stage-1 values to seed the slow phase. Profiles the time constants (and TD) on a coarse grid and keeps the RSS-minimising start (cf. expdrift_start()). The model is linear in A, B, and B2 once tau, tau2, and TD are held, so those are solved by least squares at every grid point at once: the Gram entries of the bases e1, e2 - e1, 1 - e2 for every ⁠(tau, tau2)⁠ pair follow from the column products of the two exponential matrices, and solve_grid3() solves the pairs in one pass. User-fixed values narrow the grids; the amplitudes are always solved free, as this is only a seed. Pairs with tau / tau2 > 0.98 are dropped as their bases are near-collinear, unless both time constants are fixed.

Usage

biexp_start(x, t, fixed = list(), has_TD = FALSE)

Arguments

x, t	Numeric vectors of the response and time.
fixed	A named list of user-fixed parameter values, which narrow the grids and constrain the free estimates.
has_TD	Logical; include the time delay TD.

Value

A named numeric vector of starting estimates in model order.

mnirs documentation built on Sept. 13, 2026, 1:06 a.m.