Swapping Registers on HP calculators

[n1msr]

Thank you all for taking the time to reply, and apologies for the vagueness of the question.
Also, thank you Marc for indenting the Python!

Valentin summarised my question well: "I have a 1 x 9 array A and I need the most efficient sequence of RPN steps to exchange element A(1,i) with element A(1,j).
Also, I am [still] curious how to toggle USER mode programatically, if it is possible.

Below is the code for the HP-15C SWAP code to exchange two elements i and j in a single 1 x 9 matrix A.
USER mode is on, although I am not reliant on this for the SWAP
i is stored in R3
j is stored in R4
"temp" store for the SWAP is R5

*please note that I add 1 (one) to the column (i and j) because the algorithm uses 0 (zero)
as the index to the first element of the list/matrix, whereas the 15c uses 1 (one). Changing the
algorithm to use 1 (one) as the index to the first element would save several steps!

Code:


1           \\ row 1
RCL3      \\ column i
1           \\ add 1 to column*
+
RCL g A  \\ recall ith element of matrix A: A[1,i]
STO 5     \\ store ith element of A in "temp" register R5
1            \\ row 1
RCL 4     \\ column j
1            \\ add 1 to column*
+
RCL g A   \\ recall jth element of matrix A: A[i,j]
1            \\ row 1
RCL 3     \\ column i
1            \\ add 1 to column*
+
STO g A  \\ store A[1,j] into A[1,i]
RCL 5     \\ recall "temp" to get original A[1,i]
1           \\ row 1
RCL 4    \\ column j
1           \\ add 1 to column*
+
STO g A   \\ store original A[1,i] in A[1,j] to complete the SWAP

That's it. Thank you.