Complicated Math Programming and More

[nactownag]

Howdy,

This is my first post on this board, but I am by no means a n00b when it comes to the interwebz. I'm glad I found this forum! Seems like people actually hang out here and there's lots of good information.

Now on to my question:

First, I'll kind of explain in words what I'm trying to accomplish.

What I'd like to be able to do is run the program and have a dialog box or something of the sort come up and ask me to specify what variable I'm wanting to solve for.

For example, take the equation below:




Let's say I want to solve for M, so next the program should create a new dialog box and ask me to specify the values for the other variables. So in this particular case, it would ask me (preferably all in one dialog) to tell it the value of F, N, INT, T, and k. And obviously, if I choose to solve for a different variable at the beginning, the function should accommodate for that. So if instead of selecting M, if I tell it to solve for INT, then it should ask me to specify values for F, N, M, T, and k.

I don't want this to be like where I type "abc(3500, .05, 10)" to get an answer. This is cool and useful and all but I'm trying to learn more advanced stuff. I'm sure someone here knows what I mean!

One last thing, is there a software available that will allow me to edit .89p files and the like. Surely there is a way to edit the programs I have installed already.

Thank you!

Jason
College Station, Texas

[DarkerLine]

Well, it's all possible. What specifically have you tried doing? It wouldn't help you in the slightest if we just gave you a finished program. Try it, and then ask for help with specific problems you run into. The Dialog..EndDlog and solve() commands are of course a good start.

Also, the numeric equation solver does a lot of what you want already, with the one drawback that it doesn't give exact solutions.

[nactownag]

Hey,

Yeah I've tried several different things but I always seem to get stuck. I understand that it doesn't do good to just do it all for me but I sure could use a template of sorts to work with. I'm mainly getting stuck with all the conditions that are involved. I truly believe that once I see it done right one time I will forever be cured on this disease they call confusion.

[nactownag]

Do you think this needs to be a function or a program?

[DarkerLine]

If it were a function, your input and output would generally be in the style you said you wanted to avoid. Programs are generally the ones that deal with dialogs.

So to get you started: First, you want a Dialog box. The variable you want to solve for is one of a few options, so it should be in a DropDown menu; the values of the other variables can be anything, so make them Requests. There's some tricky stuff here. First of all, everything entered into a Request is a string: so you'll have to use the expr() command afterwards to turn them from strings into numbers. Second, the result of the DropDown is a number equal to the option selected. So maybe you have a variable called "var" to determine which variable you want to solve for: if var=1, then you're solving for M, if var=2 you're solving for F, and so on (depending on the order you list them in, in the menu).

Next is the solving step. You could do this in one command, but it's slightly tricky; using If .. Then .. ElseIf .. EndIf is simpler to understand. Just check for every possible value of var, and in each case, output the result of a solve() expression that solves for the corresponding variable. Here, there's another tricky part: solve() returns an equation or several equations, but Text (the command you'll probably want to use) wants a string. So use the string() command to convert it to one.

Here's a sort of framework:


solveeqn()
Prgm
Dialog
© DropDown for variable to solve for, stored to "var"
© Request for each variable in equation
EndDlog
© Use expr() to format each variable's value
If var=1 Then
© solve for first variable, display solution
ElseIf var=2 Then
© solve for second variable, display solution
...
Else
© solve for last variable, display solution
EndIf
EndPrgm

Obviously this isn't the best code. It's repeating things that only need to be written once, and some things, like the equation, are hardcoded and therefore hard to change. Just start with doing something like this and then we can work on improving it.

[nactownag]

So then the variable I select from the drop down....won't that still show up in the requests?

[DarkerLine]

Yes. It will. What you input for it won't mean anything, but it will show up.

The only way to avoid that is to have more than one dialog. I don't know if that's worth it for you. Basically, the first thing you do is choose the variable to solve for, in one dialog. Then you have two options to do the rest. One is another chain of If .. ElseIf .. EndIf statements, with a dialog box omitting the variable being solved for in each one. This is very redundant. The other option is to build up a dialog dynamically: make a string containing "Dialog", then add on ":Request "BLAH",blah" for every variable you plan to include, then finish with adding an ":EndDlog". After that, expr() of that string will give you the dialog you want.

This last method is more advanced and may or may not be actually worth it, at this point. Also, it gives up independence from language localization, since the command Dialog is different in other languages.

[nactownag]

Sorry it's taken me a while to reply back.

Ok....here's just what I've come up with so far. I've simplified it down as far the formula goes. I figure that if I can do this with a simple formula I should be able to do it with a more complicated formula.

I'm sure there are some errors in this but I'm hopeful that it's close to being right.

[nactownag]

Or should it be more like this:

[DarkerLine]

The second approach is correct (although there are multiple valid ways of solving the problem), and both have a few syntactical problems to address. I urge you to try and fix some of them yourself by, y'know, running the program to see what happens, before reading further.



First of all, the output of DropDown is a number: either 1 (representing the first option) or 2 (representing the second option). This should be reflected in your If..ElseIf code.

Second, you can't separate statements with commas. If you want to put the solve() and Disp on one line, you can use a colon. Or you could just put them on two separate lines.

Third, Disp "x" will not display the value of x that has been solved for. It will just write the letter x. What you want to do is output the result of solve(). Which means you must either save the result of solve(): e.g. solve(...,x)->res: Disp res -- or just output it immediately: Disp solve(...,x)->res.

[nactownag]

Awesome. I just plugged the following code in and it works perfectly

[nactownag]

Also if I need to add more variables....with regard to the IfThen statements would this be appropriate?

[nactownag]

I've made an attempt at making this a lot more complicated math problem and I'm getting a "too few arguments" error.

Not sure exactly what it could be...

[DarkerLine]

You can't name a variable INT because int() is a built-in operation, and variable names are not case-sensitive. That's part of the problem.

Another problem that you'll run into is that writing M(1-F) makes the calculator think you're evaluating a function called M at the value 1-F. Write M*(1-F) instead, and similarly in all other such cases.

[nactownag]

I fixed those things but it's still throwing the error. I think that there is something wrong with the parenthesis. But I can't figure out what could be wrong....do you see anything?

[nactownag]

Got it!

[TI-newb]

is this on Ti-Basic?? i have never encountered.. 'Request' or 'Dialog'. =/

[DarkerLine]

It's TI-89 Basic. Come to think of it, I should probably move it to that subforum.