Recursive select / updates

Hi,I have a problem where i need to calculate totals in a table that are based on previous values and calculations.I am currently doing that in a function which works fine but was wondering if there is a more elegant or efficient way to do this.
Here is an example table, ordered by row no.The total is based on the previous rows. Note that the difference of a values does not always need to be 1
row | a | b | total |------+----+-------+------- + 1 | 3 | 11 | 0 | 2 | 5 | 34 | 22 | 3 | 6 | 64 | 67 | 4 | 7 | 525 | 176 | 5 | 8 | 9994 | 810 | 6 | 9 | 26216 | 11438 | 7 | 10 | 3363 | 48282 | 8 | 11 | 1147 | 88489 | 9 | 12 | 1037 | 129843 | 10 | 13 | 200 | 172234 |

Total Row 2(a2-a1)*b1 i.e. (5-3)*11 = 22
Total Row 3 (a3-a2)*b2 + (a3-a1)*b1 i.e (6-5)*34 + (6-3)*11 = 34+33=67
Total Row 4 (a4-a3)*b3 + (a4-a2)*b2 + (a4-a1)*b1 i.e (7-6)*64 + (7-5)*34 + (7-3)*11 = 64+68+44=176
Has anyone a clever solution for that problem?
Thanks for any suggestions.
Alex