auto generated data

[Dominique Michel <dominique michel vtxnet ch>]

Hi,

I use date generated by engauge-digitizer in gnumeric.
They are .csv files that look like this:

x,-35,-30,-25,-20,-15,-10,-5,0,5,10,15,20,25,30
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
0.703889,,,,,0.00141043,,,,,,,,,
0.705549,0.000706213,,0.000706213,,,,0.000706213,,,,,0.000706213,,
0.707209,,1.99214e-06,,,,,,1.99214e-06,,,,,1.99214e-06,1.99214e-06
1.40944,,,,0.00211665,,,,,,,,,,
1.41276,,,,,,,,,,,0.000708205,,,
2.10503,,,,,0.00704818,,,,,,,,,
2.10835,,,,,,,,,,0.00563974,,,,
2.11333,,,,,,0.00352708,,,,,,,,
2.81389,,0.00634595,,,,,0.00634595,,,,,,,
2.81721,,,,,,,,,,,,,0.00493751,
2.81887,,,,,,,,,0.00423329,,,,,
3.51612,,,,,,,,,,,,0.00846061,,
3.51944,,,,0.00705217,,,,,,,,,,
3.5211,,,,,,,,,,,,,,0.00634795
3.52276,,,,,,,,,,,0.00564373,,,
3.5294,0.00282684,,,,,,,,,,,,,
...
770.122,0.0141412,,,,,,,,,,,,,

The first column is the x axes, and each subsequent column represent
the y values of one digitized curve on a curves set.
The only column that have a value for each line is the first one, x.
I also have 2 other sets of curves, where the curves are not always
beginning at the first line (at x=0), so it can be missing values at
the beginning.

I can use engauge to extrapolate the missing values, but it continue
after the curve ends, in order to get a value for each point on x.
And this extrapolation after the curve ends doesn't always make sens.
I also don't know at that time if I will need it or not, but that's
another issue to be solved later. 

So, it would be better if I can use gnumeric to extrapolate those
values, but only from the first to the last value of the curves.

Is it a way to do that in gnumeric?
I experimented with the following formula:

B2=B1+((B3-B1)(A2-A1)/(A3-A1))

It work well for my purpose (even if some bezier calculation would
be a little bit better), when both adjacent vertical cells have values,
but it doesn't work when either or both adjacent cells doesn't have
value.