Creating an equation library (Updated 03-FEB-2017)

[Han]

(02-01-2017 11:24 AM)akmon Wrote:  I agree that the firs step is working on the engine of solving the system, that´s true.

In my hopes, I admit I´m nostalgic with the old Solvesys library from Hp48, 49, I inserted several equations, and the program "ate" them solving the variables amazingly, with no need to create them. So now you know which are my priorities. Of the course, managing files of equations i awesome and useful, but it´s easier to program. The main engine is the most important part of the proyect, my point of view is have both worlds for using from a way or other: the file manager stores all equations, clasified with menus, choose boxes etc. But once the equations are selected, launch the engine to solve them, or if you don´t want to use the file manager, and just only press the engine and solve some equations "on-the-fly" it could be done. The problem is the automatic creation of variables, it´s strange there is no command that extracts them from the equation.

Once the equations have been created, then extracting variables can be done using LNAME. However, one cannot enter equations into the Symb view using variables that do not already exist (i.e. entering equations that involve only global variables like A-Z is ok, but using a custom variable name that has never been created will result in an syntax error when using the Symb view). That is just a quirk with the HP Prime's non-CAS side -- you cannot enter formulas that use variables that do not exist. Using the Symb view means not having to create a brand new interface for entering functions (plus, it gives you pretty-print AND it has some basic form of syntax checking). And the Symb view's behavior is the only reason users have to first "create" non-global variables. In the end, I went ahead and enforced this rule for all variables for consistency. Another motivating factor was that for an equation library, the variables should really have some sort of description, which could be added during the variable editing/addition step.

I too loved how you could just make a symbolic expression on the HP48-HP50 series and never have to "declare" variables. From time to time, it still bugs me that it is not always the case on the HP Prime.