Multi-variable lookup tables

I'm working on a project where I have some graphs and tables that I need to program into a PLC. Typically, if it's just one input and one output, I can use Excel to do a regression and come up with an equation that will be pretty accurate. In this case, it's more complicated because I have two inputs.

Without getting into too much detail, imagine you have a curve for flow of a valve vs valve position. But instead, you have 5 or 6 different curves of flow vs position at different pressures. So for example let's say there's a 10 psi curve, a 20 psi curve, etc.

Can anyone give me some guidance on how to get something like this into a PLC? I can convert the information into a table, but from there I'm stuck.

What plc platform? That will have an influence on your options. A multi-dimensional array of either direct values or equation coefficients is the first thing that comes to mind. But your platform needs to be able to pull that off.

Keith

It's a GE RX3i. I believe it will do multidimensional arrays, but I've never used them before. Any chance you could offer a little more guidance?

Why not a function of valve position and pressure for flow? I do this all the time.
The flow will be proportional to the square root of the pressure drop across the valve. If you can figure put how much the valve is open you are done. The formula should look something like Q(x,ΔP)= K(x)*sqrt(ΔP)

The problem is, this is not that type of application. I'm dealing with hydroelectric turbines, not valves, but wanted to make the example easier to understand. What I really want is to know how to do multivariable lookup tables. Does anyone have any advice about that?