How is the SCIRun Gradient of Scalar data implemented?

[tarkpate]

I am trying to track down the SCIRun implementation for calculating a gradient vector field from scalar data on a mesh. So far as I can tell the module CalculateGradient points to the CalculateGradient algorithm, which itself points to the Vfield gradient function, which points to the VFDataT data type gradient function, which itself uses the inverse jacobian in some way to get the gradient values.

Is there documentation/citation of how the algorithm actually works mathematically to arrive at the gradient vector field?