  We consider several well-known f(R) cosmological models and constrain their
parameters, namely the deviation parameter b and the cosmological parameters
\Omega_m and h. We first obtain analytical approximations for the Hubble rate
H(z) and the luminosity distance d_L(z) in terms of these parameters, and then
test these against the observational expansion rate derived from cosmic
chronometers and the distance modulus in the HII galaxy Hubble diagram,
obtained in a model-independent way using Gaussian Processes (GP). We first
optimize the models based solely on the cosmic chronometers and then repeat
this process with a joint analysis using both the cosmic chronometers and HII
galaxies.
