@mlunin,

Since you didn’t provide any code, I’m assuming you are already familiar with writing DLLs and you are asking on a conceptual level (correct me if I’m wrong). You can have two parameters in your DLL a minimum_index and a maximum_index. Then, when you calculate your n(x, y, z) in the DLL, you check if the value is within the boundaries defined above. If it is, you keep it as such, otherwise you replace it with minimum_index or maximum_index accordingly. In pseudo-code you will do the following.

UserParamNames

if (i == XX) strcpy(data, "Minimum index");
if (i == XX+1) strcpy(data, "Maximum index");

UserGrinDefinition

minimum_index = data[10+XX]
maximum_index = data[11+XX]

index = n(x, y, z) # As defined by yourself

if index < minimum_index
    index = minimum_index
elif index > maximum_index
    index = maximum_index

XX is an integer parameter number as defined in other Grin DLLs.

The derivatives are zero where the refractive index is constant. Mathematically speaking there’s a discontinuity in the bounded function and the derivative isn’t defined at the bounds, but programmatically you can choose to either use zero or the derivative of n(x, y, z) at that position if it hadn’t been bounded (or something else). Note that I didn’t try myself, and if that’s already what you are doing, can you give us more detail as to why it doesn’t work?

Take care,

David

@mlunin,

Apologies, but I don’t quite get the problem. Can you tell me more about why you want to store previous value of the refractive index? As far as I know, for any ray, the index is calculated at every (x, y, z) step and there’s no randomness in the size of the steps. Would you mind sharing your code with us along with a sample file that demonstrate the issue?

Take care,

David