# How to graph a "free format" function

ccuny shared this question 2 years ago

Hello,

New to GeoGebra. I have tried to answer my own question looking at a number of videos, but either I find videos showing features from earlier version, of using an f(x)= definition type and I am getting really confused.

In the attached file and screenshot, you will see that I have entered some constant, destined to be used as sliders to simulate a final value called VPP In order to define VPP, I define an intermediate value called PT.

The calculations work fine (though I have not found a way to display the results as percentages and/or fractions yet), and dragging and dropping the sliders works fine, but for the life of me, I cannot get GeoGebra to simply graph VPP.

I must be missing something very simple so I apologise for the naive question.

Would you please let me know how to chart VPP? I can then introduce the sliders and simulate.

Chris

1

You're only working with numbers and VPP too is just a number and no function so it's normal it cannot be graphed. A function would be something as f(x)= VPP or f(x)=VPP x.

chris

1

Thank you.

1

Chris,

Thank you for the comment. I have reworked the file so that f(x) is defined. x is now what used to be PR. The file is attached.

The final goal is to get a display which is the same as in the attached screenshot (except for he actual values which are different). I have the following issues to resolve:

1. I need to make sure that only the top right quadrant display (i.e; Positive values for x and f(x) only. I have looked at a number of posts about this and I haven(t managed to do it. I can drag the graph so that only the top right quadrant shows, but the other quadrants are still there. Can I "eliminate" them?
2. The formula at the top does not display the way I want it (which is the way is displays in the attached screenshot. I have played with the settings (true false) in the definition, but I suspect the original author inserted the PT+(M) (that is VPP in my file) and the more or less equal to sign as a label. Still, I need to understand how the value is displayed in % which is what I want. I previous trials, I could only display it as a decimal. Here, with the f(x) definition, I can't even get to displaying a value.
3. The attached screenshot includes a dashed lines showing the x, f(x) coordinates. As you move the sliders and the value changes, the x, f(x) changes and so that dashed line and black dots display follows along. I would also like to do that but I don't know what tool allows me to add this feature.

Thank you for your assistance and please let me know if I should post those 3 issues as separate posts instead.

1

generally it's the best to split up problems, but I will look at it furhter on. I started at my computer some 10 hours ago with different tasks and it's high time to stop. I resume tomorrow!

1

Yes, that is why I asked the question. I should have done that first time and will do so for future questions. But thanks a lot for sticking with it Chris. I am going through the wiki and other posts trying to figure things out but it is slow-going, so your patience is much appreciated.

1

1 display in first quadrant: basically use the syntax If ( x > 0 && equation >0, equation). In your case you get If(x>0&&(x SE) / (x SE + (1 - SP) (1 - x))>0, (x SE) / (x SE + (1 - SP) (1 - x))). Additionally you can set the x- and yAxis to show only positive numbers. So the axes too will only display the 1st quadrant.

2 If you want to know how an author did something, open or download the file, display the Algebra or rightclik on the item (if possible) and examine the definition of the item. This displays everything what a screenshot doesn't.

3 points and dashed lines to follow is not difficult. Create a slider s for the x-coordinate tot define the point (s,0), (s, f(s)) and (0, f(s)) These are the points to connect with segments. Now you can show or hide these points as you wish.

chris

1

Thank you very much Chris. I don't have the original .ggb file I am trying to emulate unfortunately. But the formula display at the top I can work out over time. Thank you for 1 and 3: I read last night something about putting intervals in the function definition itself but I must admit I had no idea how to implement it here. Now I understand how it works. Really useful. So it the point and dash lines marker: I really did not know where to begin.

I really appreciate the help.