HP-17BII+ serial

[tomisan]

CORRECTION to my earlier post #3.

Yes indeed, when I happened to enter my own equation *correctly* into my HP-27S (and not using RAN# as it's a built-in function in the 27S), I do get the same result as other 27S owners have shown here!

Sorry for the confusion!

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As for the different behaviour of the Solver in 17BII+ and earlier models like the 27S and 17BII:

In "Technical Applications - Step-by-step solutions for your HP-27S or HP-19B calculator" there is a discussion on pages 14 and 15 how LET and GET change an equation.

..."When an unknown variable appears only once as a formal variable, the Solver can usually isolate a direct solution.

..."When the variable appears as the first argument of LET or as the argument of GET, it's not considered by the Solver in determining whether a direct solution can be found. Thus, a variable may occur many times in an equation, yet only once formally. In these instances, a direct solution may be found, but it will not normally be "correct" mathematically."

This doesn't fully apply to the HP-17BII+ and here lies much of the confusion I believe.

**Example 7 (from page 15 in Technical Applications)

A=G(A)+1

Enter the equation, press CALC and CLEAR DATA
Press A and
27S will display A=0
17BII+ will display A=1, apparently the correct answer.

Press A again and
27S will display A=1 which is what we might expect. Each press of A will increment A by 1, so 27S will show 2,3,4,...

However, 17BII will not increment A, A=1 is the final solution. This is not what we might expect!

**Example 8 (from page 15 in Technical Applications)

Q=L(A:A+1)

Enter the equation, press CALC and CLEAR DATA
Press Q and
27S will display Q=0
(However, if A is initialized first with A=0, then we get Q=1)

17BII+ will display Q=1, apparently the correct answer (no initialization necessary).

Further presses of Q on the 27S will display Q=1,2,3,... what we expect.

However, 17BII+ will display Q=3,5,7,... not what is expected!
(For each run, the 17BII+ will do an additional evaluation of the expression).

One way to simulate the behaviour of 27S is to enter
Q=L(A:A+1/2)
then store -0.5 in A before the first run.

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According to Cyrille de Brébisson the Solver in 17BII+ is the same, but transcribed in C. The "direct" solver part however seems to use a slightly different algorithm.
http://www.hpmuseum.org/cgi-sys/cgiwrap/...ead=134189

I just wish that HP would have published a ""Technical Applications - Step-by-step solutions for your HP-17BII+ calculator"!