model
The 1996 Ottaviani-Horton-Erba ITG/TEM mode transport model [1]
has two versions, distinguished by whether or not the transport is
thresholded by a marginal stability gradient. The thresholdless version
is selected by setting switch = 0. The thresholded version is
selected by setting switch = 1, and it is assumed that the
threshold has been calculated elsewhere.