how do I implement a polynomial control input

[bcglaxer]

I'm using Labview 8.5 and the Control Design and Simulation toolkit or module or whatever it is. Anyway, I'm trying to build a controler where my desired input (Yd) is a function of a measured variable (X, see attached picture). Do I have to discretize the polynomial into a lookup table, or can I implement the polynomial as is? And, whichever way is the way to go, which VIs would I need to do so?

Thanks,

Brian

[MikeS81]

Hi Brian,

i don´t understand what you need? Do you try to build a polymorphic vi, like "Write to Spreadsheet File"?

Mike 

[TCPlomp]

In the Mathematical VIs there's a palette for polynomial calculations. These are not available in LabVIEW base.

I think you need Polynomial Evaluation:

Ton

[smercurio_fc]

You can also use the formula parse functions (under Mathematics -> Script and Formula -> Formula Parsing), allowing you to enter a formula like "ax^2+Bx+c" There are a few examples that ship with LabVIEW that show you how to use these functions.

[CMal]

bcglaxer,

If your polynomial coefficients are known, then you can do something like the attached screenshot with a Simulation loop.  Simply multiply and add the values.  You would probably replace the 'a', 'b', and 'c' controls with contstants, and the 'x' control would be replaced with whatever code you are using to dermine the value of 'x'.   Is this what you had in mind?

Chris M

[bcglaxer]

Thanks for all the suggestions! There certainly are a lot of ways to go about this. I've used Polynomial Evaluation for now but may try the other approaches in the future if I run into problems. Thanks again,

Brian