LToolsSetLambda corresponds to the
SetLambda function in LoopTools.
See ?LoopTools`SetLambda for further information
regarding this LoopTools symbol.
LToolsSetLambda is also an option for
LToolsEvaluate that sets the numerical value for the IR
regularization parameter \lambda^2.
Setting \lambda^2 to -2
or -1 will make LoopTools return the coefficients of the
1/\varepsilon and 1/\varepsilon-poles respectively. The value
0 yields the finite part of the integral where IR
divergences are regularized dimensionally.
When \lambda^2 is set to some
positive value (say 2.), LoopTools will return
the finite part of the integral with IR divergences being regularized
using a fictitious mass. The result will naturally depend on the value
of \lambda^2.
It is important to keep in mind that for \lambda^2 = -1 LoopTools also returns the UV-pole, although this not so clearly stated in the official manual.
Notice that the option LToolsSetLambda is ignored, as
long as LToolsFullResult is set to True.