Calculate a diagonal total using dynamic arrays on Excel

Question

I need to calculate a diagonal total of numbers in a dynamic array on an Excel sheet. The number of columns will increase but there will always be seven rows in the tableau, so I need the formula to automatically adjust to the number of columns in the array.

Example of array and results underneath

In the example results the first column has only one figure to total, (215). The second needs to add (249) and (246) giving a result of (455) and so on.

Obviously I can just create a series of formulae to add the relevant cells in the results, but that doesn't meet the need for the formula results to adjust to the size of the input array.

I've been scratching my head over whether there is a clever matrix solution to this, but my maths isn't good enough.

Subcontract	Current month	(215)	(249)	(39)	(139)	(267)	(130)	(356)	(126)	(193)	(403)
	Next month	(206)	(205)	(40)	(190)	(225)	(205)	(274)	(120)	(261)	(381)
	Month + 2	(176)	(189)	(50)	(135)	(279)	(156)	(219)	(129)	(241)	(304)
	Month + 3	-	(8)	-	(23)	-	-	(19)	-	-	(26)
	Month + 4	-	-	-	-	-	-	-	-	-	-
	Month + 5	-	-	-	-	-	-	-	-	-	-
	Month + 6	-	-	-	-	-	-	-	-	-	-
		(597)	(650)	(130)	(487)	(771)	(491)	(868)	(374)	(696)	(1,115)
Subcontract out of stock		215	455	420	367	516	491	863	555	532	813

In the original spreadsheet the Subcontract data is in the form of an x by 7 dynamic array, in this case 10 columns by 7 rows.

"Subcontract out of Stock" is what I'm aiming for. In each column it is the total of current month plus "Next month" from the previous column (if it exists) plus "Month + 2" from two columns before (if it exists) and so on. Each output has the sign changed.

OK, I did this and it gives me what I needed:

  =MAKEARRAY(1,COLUMNS(C130#),
   LAMBDA(r,c,
      OFFSET(C130,r-1,c-1)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),1,-1)),0)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),2,-2)),0)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),3,-3)),0)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),4,-4)),0)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),5,-5)),0)+
      IFERROR(N(OFFSET(OFFSET(C130,r-1,c-1),6,-6)),0)
   )
)