Equation stored in variable, then used by Solver

[Alfon]

Is there a way to store an equation in a variable, then use the solve application to retrieve this equation from the variable and then solve it?

[Han]

You can save the equation in a string. Likewise, I would consider a separate string for the variables.

E.g.

Code:


// formula: F=ma; we'll use the global variable F and create m and a as needed
vars:={ "m", "a" }; 
eqns:="F=m*a";

// initialize solver
local cmd,i, n:=SIZE(vars);

for i from 1 to n do
  cmd:=vars(i) + ":=0"; // set initial value to 0;
  CAS(cmd); // call CAS to evaluate cmd as if run from command line
end;

E1:=eqns; // set E1

// … code here to start the app, see STARTAPP() or STARTVIEW()

// clean up, if needed
for i from 1 to d no
  cmd:="purge(" + vars(i) +")"; // create a purge command
  CAS(cmd); // purge the variable
end;

These routines can easily to combined into a solver app to build an actual equation library with complete support for custom equations and variables. I'm currently working on one, but have been sidetracked with several other projects…

[Angus]

Han, is that part of program code? What did you show? How would you use it? Do you -have- to store equations to a global, capitalized variable F? Do you assign the variable list m,a and the equation prior to program start?

A working example with additional comments would be beneficial. Thanks.

[CR Haeger]

I have saved formulas into CAS variables, defined solve.E1:='CAS variable' (a formula) then used Solver.

Here is a thread about this: http://www.hpmuseum.org/forum/thread-955.html

Best,
Carl

[Angus]

Thank you, I remember your thread. You don't use any strings, I see? Copying over a note to the cas is not really user friendly. :-(

I had the feeling Han tried to add more automation on the one hand and on the other I feel like that is an example to learn to avoid issues when programming the calculator.

What is about string usage and no string usage. I studied the patch notes and did not notice any changes concerning these topics (that is data handling) so there is a need to get used to how things are now. They are likely to last.....
I might be old or I might not have enough time for the calculator there is even the chance of being too stupit, but I did not really understand this device. I can play with it, I find interessting aspects, but once I really need it I get stuck and can't find the right way to work with it. It still did not become a tool, it is still a toy which frustrates me.