Populate table row with rate changes with one formula

Question

I've got this Exhibit A in brute force for a rate that is halved after 10 minutes

#+NAME: ratetable
| 0 min | 10 min | 20 min | 30 min | 40 min | 50 min |
|  20.0 |    10. |     5. |    2.5 |   1.25 |  0.625 |
#+TBLFM: @2$2=@2$1/2::@2$3=@2$2/2::@2$4=@2$3/2::@2$5=@2$4/2::@2$6=@2$5/2

What I'd really like is a way to put in just one starting value in the second row/first column and have the rest of the row populated without all the individual formulae per cell. Any ideas/docs talking about this sort of "amortize(?) the whole row/column" would be appreciated.

Answer 1

You can use a range formula for cases like this. The relevant section in the manual, which you can get to with C-h i g (org) Field and range formulas, says:

‘@1$2..@4$3=’

Range formula, applies to all fields in the given rectangular 
range.  This can also be used to assign a formula to some but not 
all fields in a row.

That, combined with relative references (C-h i g (org) References) , allows to write the above set of formulas as a single formula:

#+TBLFM: @2$2..@2$> = @2$-1/2

In words: for every cell in the second row @2, starting with the second column $2, and ending with the last column $>, set its value to be the value of the cell in the second row but the previous column $-1, divided by 2.