I was bored and found a HP-27S

[Dave Britten]

(06-11-2014 08:04 AM)Thomas Radtke Wrote:  I assumed some kind of array would be required, but I was wrong (at least on the 20S), sorry.

Not being an expert with the solver, I tried to construct an infinite loop this morning:

(1) A=sigma(I:1:10:0:I) gives 'solution not found'

(2) A=sigma(I:1:10:1:L(I:I-1)) gives 45

In (2), it appears, 'I' cannot be decremented and L(I:I-1) evaluates to I-1. Further investigating this:

(3) A=sigma(I:1:10:1:L(I:I-1)+I) gives 100 (apparently 45+55)

Sorry again if I've just shown my ignorance ;-/.

(feel free to fork this into another thread if it's of any interest)

The final paragraph on page 25 of the Technical Applications book mentioned earlier explains that the loop counter, start, and end values are copied to separate memory locations that can't be modified directly once the loop starts, so I think your conclusion that an infinite loop is impossible is probably correct. (Unless there's some other mechanism waiting to be abused. Forcing an iterative solution and constantly modifying the variable being solved for with L(), perhaps?)