Issue with CAS solver function involving passing strings to the variable position.

09302020, 04:06 PM
Post: #1




Issue with CAS solver function involving passing strings to the variable position.
I am writing a program that asks what the user would like to solve for and then pass that into the CAS Solve function. The program look like this:
[code]//Amplitude export Amplitude() BEGIN Local Find,Find_1,variables,Answer; Local Â,K,τ,ω; print(); //K=5, Â=0.0355 τ=10 ,ω=3.1415 ,E=.5 ,A=7 A:=0; CHOOSE(A,"Which Amplitude?","Final","Initial"); if A==1 then variables:={"Â","K","τ","ω","E","A"}; input({{Find,variables,{56,15,0}},{Â,[0],{10,20,1}},{K,[0],{10,20,2}},{τ,[0],{10,20,3}},{ω,[0],{10,20,4}},{E,[0],{10,20,5}},{A,[0],{10,20,6}}}); Find_1:=variables[Find]; Find:=Find_1; Answer:=CAS("SOLVE(Â=K*A/(sqrt((1(τ*ω)^2)^2+(2*τ*ω*E)^2)),Find,1)"); print(Answer); end; END;[code] When I run this it returns "Error: Constant function" I have tried expr(Find) and also EVAL(Find) but both options failed to work. 

10012020, 10:07 AM
Post: #2




RE: Issue with CAS solver function involving passing strings to the variable position.
I'm just a novice, but it looks like you mixing text and variables in the string expression. Try something like:
Answer:=CAS("SOLVE(Â=K*A/(sqrt((1(τ*ω)^2)^2+(2*τ*ω*E)^2))," + Find + ",1)"); 

10012020, 12:10 PM
(This post was last modified: 10012020 12:21 PM by Grayhek.)
Post: #3




RE:Issue with CAS solver function involving passing strings to the variable position.
(10012020 10:07 AM)Gene222 Wrote: I'm just a novice, but it looks like you mixing text and variables in the string expression. Try something like: So it works better than before in that it doesn't return an error but it doesn't evaluate the equation. I normally ran into that problem when I didn't us the program in the solver app but I checked and made sure I was in the Solver app and it still was not running properly. I ran it in the CAS environment and it returned an error. Code:


10012020, 04:38 PM
(This post was last modified: 10012020 04:47 PM by Gene222.)
Post: #4




RE: Issue with CAS solver function involving passingstrings to the variable position.
I don't know how to get SOLVE or fsolve to solve your equation. Some comments on your first program are:
(1) Your choose variable A is the same as your variables[6] which is also defined as A. (2) I tried using fsolve instead of SOLVE, but it gave {} which I think means fsolve could not find an answer for the initial guess. (3) I tried exporting the solve variables, but that did not help. Below are the changes I made to your program in trying to get the program to work. I predefined your list variables, because I got tired of inputting the values in the INPUT screen. Sorry I could not help you. PHP Code: EXPORT Â,τ,ω,A1,Answer; 

10012020, 09:55 PM
Post: #5




RE: Issue with CAS solver function involving passing strings to the variable position.
yes I tried that as well period on my calculator I already had them as global variables in another program labeled load_variables (). I just put them in as local variables so that people would not get lost reading the program. I may have to resort to waiting multiple If statements/Cases or figure out how to utilize the solver app. I'm reluctant to do this
1) because I don't know how to program utilizing an app 2) because multiple If statements would clutter up the code. 

10012020, 10:43 PM
(This post was last modified: 10022020 05:57 PM by Gene222.)
Post: #6




RE: Issue with CAS solver function involving passing strings to the variable position
You might have a problem with the names you used for your variables. See the following posts below.
HP Prime Solver Variables Issue Programming solve function I also have had problems with expressions that included trig functions that gave multiple answers, where I had to either use an initial guess that would narrow the search for a solution, or put a limit on the solve variable such as 0.0001..2*pi. I also had problems where the variables would give a division by zero error or where the change in the parameter variables would not significantly change the solve variable, so that fsolve could not find a solution. In one case, I ended up replacing fsolve with a trial and error/bisection method in order to find a solution. 

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