Enter formulas to compute on-the-fly new output variables

We want to be able to visualize new variables defined as functions of the output variables in the dataset by entering some standard mathematical formulas.

I also attach here a new dataset rt50.tar.gz coming from a 1D coupled reactive transport simulation with 50 grid elements and 57 time steps. In input we have just the spatial coordinate "x" and "time"; in output several variables: C, Ca, Cl, Mg, pH, Calcite and Dolomite.

Some examples of the formulas I would like to be able to compute:

1. H = 10^-pH
2. MgCa = Mg/Ca
3. logMgCa = log10(MgCa)
4. SI_Cc = log10(C x Ca/{100.8 x (4.69E-11 + H)})

and so on.