(DM42) Matrix exponential

[Werner]

Hi Gjermund,
adapted mine as well so that the number of expm1 terms could be easily changed.
I switched to 6 i.o. 10 squarings though - for the 42S version (where it matters most), that meant two fewer matrix multiplications (6 terms, 6 squarings give the same accuracy as 4 terms, 10 squarings), and for the DM42 it doesn't matter (6 terms and 14 squarings or 10 terms and 10 squarings).
And, still all in the stack ;-)
(I'd like to make it independent of the calculator's precision, but that proves to be a bit of a challenge, only using the stack ;-)

00 { 98-Byte Prgm }
01▸LBL "E↑M-I"
02 ENTER
03 FNRM
04 LN
05 2
06 LN
07 ÷
08 6
09 +
10 IP
11 X<0?
12 CLX
13 X<>Y
14 2
15 RCL ST Z
16 +/- @ avoids overflow..
17 Y^X
18 ×
19 14 @ 6 for 42S
20 RCL ST Y
21▸LBL 05 @ X := (X/Y+I)*Z, keeping YZT
22 RCL÷ ST Y
23 XEQ 01
24 RCL× ST Z
25 DSE ST Y @ DSE n, skip when n=1
26 DSE ST Y
27 ISG ST Y
28 X=Y? @ aff
29 GTO 05
30 R^
31 X<>Y
32▸LBL 04
33 ENTER
34 +
35 LASTX
36 STO× ST X
37 +
38 DSE ST Y
39 GTO 04
40 RTN
41▸LBL 01 @ add I
42▸LBL "M+I"
43 EDIT
44 ^
45▸LBL 02
46 ↓
47 SIGN
48 X<0?
49 +/-
50 RCL+ ST L
51 →
52 FC? 77
53 GTO 02
54 EXITALL
55 END

Cheers, Werner