Sum of matrix elements

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Summary:

Yes, there's a forum page covering this, no, it did not help.

Sum of matrix elements

Mewcancraft 03 Sep 2015 06:08

Hi there,

I am programming a game that has a board sort of like chess. You move around a cursor and different buttons do different things (lol, I'm so vague). The board has an underlying matrix that has a slot for each square on the board.

To know if the player won or not, I need to check the sum of all elements in the matrix to see if it is equal to the goal number. It'd make sense to do that every main loop. Now here's the fun part: there is no sum( command for matrices. It doesn't make much sense to me, but you have to write your own formula for this. I know there's a wiki page on this, but the formula stated there seemed wrong to me after studying the Matr>list( command. It also doesn't work.

I tried making my own formula for calculating the sum of all elements in a matrix: cumSum(cumSum([A])^T). This gives you a matrix from which you need to take the value in the very last slot. It does the job, but it makes the game loop really slow, so I'll need something faster. Anyone any suggestions on what I should use?

Last edited on 03 Sep 2015 14:25 by Mewcancraft Show more

Re: Sum of matrix elements

Silver Phantom 03 Sep 2015 15:04

this should help:
link

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Re: Sum of matrix elements

Trenly 03 Sep 2015 15:27

he said

I know there's a wiki page on this, but the formula stated there seemed wrong to me after studying the Matr▶list( command. It also doesn't work.

Re: Sum of matrix elements

Silver Phantom 03 Sep 2015 15:30

ahh, sorry, i missed that part.

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Re: Sum of matrix elements

Trenly 03 Sep 2015 15:44

Nbd. We are all just here to help. Just thought you might not have seen it

Re: Sum of matrix elements

Silver Phantom 03 Sep 2015 15:49

I just ran it on my calc and I don't see how it doesn't work.

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Re: Sum of matrix elements

Trenly 03 Sep 2015 17:16

idk either, unless hes running on a ti-83

Re: Sum of matrix elements

lirtosiast 04 Sep 2015 01:45

What is the problem when you try to use the routine on the page? It works fine on my calc and Silver Phantom's.

Re: Sum of matrix elements

Mewcancraft 04 Sep 2015 14:38

I experimented some more with Matr>list, and it seems like the formula on the wiki (Matr>list(cumSum)^T, Ans(1), L₁) is wrong by using Ans(1) as the second argument. It's that or the person who wrote the wiki page didn't think it through too well. It should be Ans(amount of rows) instead, which I figured out myself and it fixed the problem I was having with that formula. What might have happened is that the person who wrote the page worked with a Matrix with only 1 row, which is stupid if you're trying to teach people about a formula for matrices, TWO-dimensional lists.

That aside though, it's still not fast enough. I have been thinking about other methods to use (e.g. checking if a specific value exists somewhere in the matrix, which I haven't found a way to yet), but with no success so far… Thanks for all the feedback so far though, it always helps to come up with new ideas.

Re: Sum of matrix elements

Silver Phantom 04 Sep 2015 14:51

Well, Ans(1) was to obtain the number of rows given from Dim([A]), which outputs {rows, columns}

Would it be too slow to use seq( or try to augment each row into a list?

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Re: Sum of matrix elements

lirtosiast 04 Sep 2015 15:24

Often in speed-critical situations list operations are faster than matrix operations. Consider using a list of R*C elements rather than a matrix of dimensions RxC, and access the elements in row Y, column X using L1(YC+X). This will cause individual accesses to be slower but summing the

In your case there is a simpler solution: you can store the sum in a counter, and update the counter whenever you update the matrix.

Re: Sum of matrix elements

Mewcancraft 10 Sep 2015 17:29

Omg, how did I not think of that? A counter that updates with the matrix! That's such a great idea!

Re: Sum of matrix elements

Trenly 03 Sep 2015 15:02

This code I think should work:

SetUpEditor L1,L2
{0->L2
1->A
Repeat A>3   //set this number to the number of columns in your matrix. see below for other info
Matr▶list([A],A,L1
A+1->A
sum(L1)->L2(dim(L2)+1)
End
Disp sum(L2)

To automatically determine the size of the matrix use:

//code before this
1->A
dim([A]->L1
L1(2)->X
Repeat A>X
//code after this

If you're using an 83+ you Could use two Repeat commands nested inside each other. That got a bit buggy for me.

Last edited on 04 Sep 2015 21:13 by Trenly Show more

Re: Sum of matrix elements

lirtosiast 04 Sep 2015 15:17

Two Repeat commands? Why?

0
For(C,1,sum(dim([A]),2
Matr▶list([A],C,L1
Ans+sum(L1
End
Ans

The wiki routine is better though, and I don't know how it currently doesn't work on Mewcancraft's calc.

Last edited on 04 Sep 2015 15:19 by lirtosiast Show more

Re: Sum of matrix elements

Trenly 04 Sep 2015 21:12

If you didn't want to use Matr>List you would have to do

Delvar L2
SetUpEditor L2
Dim([A])
Ans->L1
For( A,1,L1(1))
For(B,1,L1(2)
[A](A,B)->L2(dim(L2)+1)
End
End
Disp sum(L2)

However I personally would use

Delvar L2
SetUpEditor L2
dim([A]
For( A,1,Ans(2)
Matr>List([A],L1
sum(L1)->L2(dim(L2)+1
End
Disp sum(L2)

I'm sure your code is the optimized version of this

Last edited on 04 Sep 2015 21:13 by Trenly Show more

Michael (guest) 07 Sep 2015 19:29

You could also do this:

Delvar Bdim([A]
For(A,1,Ans(2)
Matr>List([A],L1
B+sum(L1 -> B
End
Disp B