HP15C: Useful indirect addressing for Solve - Custom TVM

[Pekis]

Thanks to an idea of Karl Schneider published in this forum in 2003, this deserves to be included in the owner's handbook about Solve:

"Solve can solve for any register involved in the called subroutine"

To solve for the x register:
LBL A
<Use the x value, along with other values or registers>
...
<Result in x register>
RTN

(Guess) SOLVE A

To solve for a storage register in particular:
LBL A
STO <n> (Store x value in R<n>) or STO (i) (if i is preloaded with value <n>)
...
<Use the R<n> value, along with other values or registers>
...
<Result in x register>
RTN

<n> STO i (If "STO (i)" is used in the subroutine)
(Guess) SOLVE A

The use of "STO (i)" allows to choose which register to solve for in a calculation involving one or more registers