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HP Forum Archive 14

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HP 33s - Equation Solve
Message #1 Posted by Dan on 24 Mar 2005, 5:55 p.m.


I have a 33s and when using the SOLVE for an equation I get SELECT FN instead of continuing with unkown variables.

What am I doing wrong?


Re: HP 33s - Equation Solve
Message #2 Posted by bill platt on 24 Mar 2005, 6:27 p.m.,
in response to message #1 by Dan


Read the manual closely here: you must be in the equation list when you push solve, if you want to solve an equation in the equation list. If you are looking at the stack (just in normal calculator mode) and you push solve, then the machine will solve a program that is saved in the program space. Same thing goes for Integrate--it works the same way. THe machine is asking you for the program label (a letter) that identifies the program that you want to solve.

Remember, you have 3 logical spaces in this machine:

1. Keyboard, Calculator (stack) 2. Program 3. Equation list.

The variables (which are really storage registers) are available in all three logical spaces.

The program space can be interactive with the stack and with keyboard calculation, whereas the equation list can only take registers, operate, and then write to registers and/or the stack, but cannot be interactive with the keyboard control of the user.

Remember, too, that you can use equations inside programs--but that these are in the program logical space--not in the equation list, and so their interaction follows the same rules as programs. And also, the solve function will solve either an RPN expression, or an equation in a program--it is very flexible.

One more thing: you are also allowed to program the "solve" function inside a program--and it can solve an eqwuation that is saved in that program, or another program inside hte program space. There is just no way to get at the equation list from a program.

Best of luck,

And you should see some useful stuff in the archives about nuances of solving.


Edited: 24 Mar 2005, 6:37 p.m.

Re: HP 33s - Equation Solve
Message #3 Posted by dford on 25 Mar 2005, 10:25 a.m.,
in response to message #2 by bill platt

Thank you Bill.

Struggled with this for some time. The problem I found was that I was brining up the equation from the equation list and hitting ENTER to "place it on the stack". I found this is not correct. By brining up the equation in the list with the equation in the X register and then pressing the SOLVE button I am now able to solve for the Unknown variable.

Thank you again for your prompt reply.

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