LastXY Register for WP34S

[Dieter]

(12-01-2014 05:44 AM)BarryMead Wrote:  What if (ALL NON-COMPLEX DIATIC OPERATORS) saved both X and Y, by calling the setlastXY() function instead of the setlastX() function then one could recall either X or XY, by choosing RCL L or CPX RCL L.

Great idea, Barry — I was about to suggest exactly the same. ;-)

Indeed, there already is a pair of LastX/Y registers: L (Last X) and I (LastY). Currently register I is only used in complex mode to save the imaginary part of the last argument, i.e. the last value of Y. So using register I generally for LastY (i.e. also for real functions with two or more arguments) should be easy.

This would only affect programs that use register I for other purposes. Which is not a good idea anyway (using A–D, L, I, J and K generally is discouraged as these registers may be used by the 34s for other purposes). The impact on existing programs would not be greater than with previous updates, e.g. the change in the way the incomplete Beta function expects its arguments on the stack.

And no, I do not expect a complex LastXY with two more registers saving LastZ and LastT, nor a LastXYZ for functions using three arguments. Although a "Last stack" command would be a nice idea. However, if this is really required it can be done using the current STOS and RCLS commands.

Dieter