# Anisotropic BSDF formula in Cycles

When you read formula regarding anisotropic GGX, for example here, you notice that the formula contains two roughness parameters for horizontal and vertical roughness. However, Cycles has only one roughness parameter but instead has another parameter named "Anisotropy." How exactly does this "Anisotropy" parameter mapped to the original formula with two roughness parameters?

Link to the corresponding code or shader is also greatly appreciated, as I'm not familiar with the code base.