I have to use document and explain how spline() works and though I am familiar with gaussian decomposition and can see that working, I am missing something on sig and p.

sig actually seems clear because is the result of the second derivative equation that spans the two intervals, but because i don't fully understand how p was developed I am unsure of sig.

That and the name 'sig' appears to reference something that doesn't stand out for me.

Does anyone have the time or spirit to give me a bit of help in understanding how these two vars were developed from the equation?

Thinking about it, maybe it is how the the non-zero first derivatives are handled. I am just missing something.

I do get the back substitution and if I could get a clean idea of these two, I think I would be ok.

Thanks, Don