How to pass a mathematical expression to a function

→ **MyCalcs** profile · by **GuardedAirplane** » 13 Nov 2015, 05:13

I was trying to write a program on my Ti-Nspire CX that would make use of the nsolve() function; however, I cannot seem to get nsolve() to accept the input equation. I have the calculator request a string from the user. I have tried directly referencing the input string in nsolve() and also tried using the expr() function to convert it to an expression. If anyone could offer advice, it would be much appreciated.

My calculator programs · by **Adriweb** » 13 Nov 2015, 05:23

You must be using a wrong syntax because nSolve(equation,variable) works fine.
For example: nSolve(x^3=26,x)
No need of a string.

Full syntax : nSolve(Equation, Var[=Guess], lowerBound, upperBound)

→ **MyCalcs** profile · by **GuardedAirplane** » 13 Nov 2015, 05:29

Can you spot the error?

Code: Select all: Define LibPub ensolve()= Prgm :RequestStr "Enter the function",function :RequestStr "Enter the variable",variable :Disp nSolve(function, variable) :EndPrgm

My calculator programs · by **Adriweb** » 13 Nov 2015, 06:25

I'm not sure you can do that on a Nspire (CX) non-CAS... because if you write Request instead of RequestStr, which is what is supposed to be done, it'll evaluate the x variable because of the non-CAS math engine, so there won't be any correct function to solve...
And if you try to expr() it within nSolve, you're just postponing the problem

You could do a Request on the equation and save it to func(x) for example, but then you'd lose the custom variable.
(but at least nSolve(func(x),x) would work, I tested that)

At this point, doing it with Lua instead of (in conjunction with, rather) TI-Basic would work around those stupid non-CAS limitations.

→ **MyCalcs** profile · by **Bisam** » 13 Nov 2015, 06:43

Of course it can be done... but you have to work your way to it !

As Adriweb said, you have to use expr(...) but it has to be done in last position.
Something like below should work :

Code: Select all: Define LibPub ensolve()= Prgm :RequestStr "Enter the function",function :RequestStr "Enter the variable",variable :Disp expr("nSolve(" & function & "," & variable & ")") :EndPrgm