Redshift- How to use previous row's calculations in current row

I am using redshift to determine projected inventory for next few week. I have receipts, current inventory and forecast. ei= ei(previous row) + receipts - forecast wk bi r f ei 1 100 20 80 40 2 50 0 3 30 15 15 4 40 14 41 5 10 31 create table ra_analytics.Test_1Test (wk int, bi int ,r int ,f int ,ei int); insert into ra_analytics.Test_1Test values (1, 100 ,20 ,80 ,0); insert into ra_analytics.Test_1Test values (2, 0 ,0 ,50 ,0); insert into ra_analytics.Test_1Test values (3, 0 ,30 ,15 ,0); insert into ra_analytics.Test_1Test values (4, 0 ,40 ,14 ,0); insert into ra_analytics.Test_1Test values (5, 0 ,0 ,10 ,0); select * from ra_analytics.test_1test order by wk --Update first week of inventory update ra_analytics.test_1test set Ei= bi+r-f from ra_analytics.test_1test where wk=1 --for next weeks inventory using lag function select wk, bi, r, f, lag(ei,1) over(order by wk) +r -f as endinv from ra_analytics.test_1test order by wk