Register to reply

What is wrong with my summation formula?

by DerekZ10
Tags: formula, summation
Share this thread:
Mar7-14, 01:29 AM
P: 4
Im trying to find a general formula I can store in my calculator that can find the number of onto (surjective) functions exists for a relation of when M is mapped to N.

I can't seem to find a nice formula for it, but based on the below material I will show you what I have developed.

From: Discrete Mathemeatics and Its Applications 7th Edition Rosen pg. 561

From: Discrete Mathemeatics and Its Applications 7th Edition Rosen pg. 512

Random Chegg Problem from Google Search I'm using to verify with:

Here is what I've formed, written out:

In the TI nSpire CX CAS, it's written like this:

And as you can see, the chegg problem I'm trying to verify it with doesn't match!
But I think it should! If I manually iterate the function like so:

The values are correct and what Chegg is showing. What have I done wrong in my equation?
Phys.Org News Partner Mathematics news on
Heat distributions help researchers to understand curved space
Professor quantifies how 'one thing leads to another'
Team announces construction of a formal computer-verified proof of the Kepler conjecture
Mar7-14, 02:00 AM
P: 477
Did you check that your summation formula matches the version that doesn't use sigma notation? i.e are all your ##m##s and ##n##s where they're supposed to be?
Mar7-14, 02:29 AM
P: 4
Wow, good call! I don't know how I constantly was missing that the (m-k) portion that should have been (n-k). And I even had it right in the non iterative equation.

Register to reply

Related Discussions
Summation formula help Precalculus Mathematics Homework 2
Ok...then since I am wrong then formula for torque is wrong Introductory Physics Homework 5
Help on prooving a summation formula Calculus & Beyond Homework 4
Summation Formula help Calculus & Beyond Homework 1
What is the summation formula? Set Theory, Logic, Probability, Statistics 6