You may be interested in the attached file. From your text I understood that you'd like to provide 1 and 3.2 and are looking for a function to give you the 0.2.
But the program you show performs a simple normal interpolation.
Furthermore you wrote that you'd like to use lienar interpolation, but you program uses splines (difference between cspline and lsline is only the behaviour at the ends - both are cubic splines).
You find linear interpolation in the attached file.
For further discussion it would be more helpful if you provide yor Mathcad sheet anmd sample data. You may have to zip the file before thos system here would accept it as attachment.
If your goal really ist f(1, 3.2)=0.2, you would have to explain what should hapen if you enter f(1.12, 3.4)=?
And which result do you expect in case of this data (0.2 or 1.0)
I can think of a lot of situations where the result would be quite ambigous. After all you can demand that the row- and column headers afre in ascending order (you can always force that unless we have two identical values which would be nonsense anyway) but you sure can't demand that all rows and all columns of the data are in ascending or descending order.
Here is a quick hack using normal interpolation from my toolbox and a solve block to give you the value of the top row.
If there are more solitions, the guess value decides which one you get.
