# SCISNAP GAMES EVENT! hosted by u39902fh

What do you mean by label?

Click the + on the top of the block while editing it, click 'label fragment'

Oh, I see. That's very cool! Also I know this isn't related but how do you reverse a summation? Bing AI couldn't figure it out, I've been really curious.

i'm starting after school (in abt 3 hrs)

Could you give an example of a “summation” you’d like to “reverse”? (and what do you consider reversal?)

I'm talking about that thingy with the greek letter sigma in the middle.

I do:
x
Σ i
i=1

where x equals 10 and then I get 55.

And I want to get a summation that gives 10 if x=55.

Oh! you mean the inverse!

So that's what it was called? Good to know.

You're welcome.

(Inversing is where you flip the X and Y component. (ie log(x) v. 10^x, sqrt(x) v. x^2, etc.))

So how do you do it?

(My School blocks Stack Overflow, so I don't know what it says.)

I didn't understand it. Can you write an example using the summation I gave you?

I'm just in precalc. I haven't learned it yet.

Oh. Well I'm sure qw23 would know.

Hey, @qw23, you know how to do the inverse of a Summation?

Well I can't think of anything interesting to do for this since SciSnap really is for representing data form science experiments.

I noticed your response only just now. I take it you’re looking for a general method to calculate the inverse of any function involving some kind of summation.

There is no such general method. Just like there is no general method to solve any equation, or set of equations.

For some summations the inverse can actually be analytically calculated. In your example, y = 1 + 2 + … + x = (x + 1) . x / 2, and reversing this is equivalent to solving x in the following quadratic equation: x2 + x - 2y = 0.

If an analytical approach isn’t available, you may try a numerical approach, or trial-and-error.

Oh.

I have some ideas!

Ideas
• Use the input block (found in Sensing category), to create games that feature choices or menus.

• Use PlotPad. This isn't some external plugin or something, it just turns a sprite into a plotting area.

• Play with ImagePad. Hopefully you can pick up something cool from ImagePad.