Fitting second series to known curve

[Emily.Marino]

I have one known series with a polynomial-like trend. I would like to
create a second series with the same X values but Y values for which
only the minimum and maximum values are known. The values in between
would fit the curve of the first series. Is there any function that
would allow me to do this?

Thanks in advance for any help as it is greatly appreciated!

 

[Bernard Liengme]

Please explain further