Hello,

I have small problem with 2-dimensional table. I have to cear some it's values to 0. You can see them on the attachment (x). I know how to clear values below or above the main diagonal but with this I have some problem. Coud you give me some tips?

Assuming this is gauss so assuming allowed *elementary row operations and no row exchanges

reduced 3x3 example:


4x4



and etc for nxn matrices

You can also see that R2 can null out R10, R3 can null out R9, etc effectively giving you rows 1-6 and with rows 7-10 being all zeros.

I don't know what Gaussian transformations exactly are (you mean this: http://en.wikipedia.org/wiki/Gaussian_elimination ?) but if I undestand your examples well after celaring elements which I ticked by X rest of elements can change their values? I don't want to have this. Fo example whole elements of table has a random number and I want set to 0 only elements which I ticked by X.

Here is an example of clearing elements under main diagonal:

Isn't it just a simple case of having the right If statement then, when iterating the cells:

Int n = Table.dimensions();

FREPD(x,n) FREPD(y,n) {

if (y>x && y<n-x && x<n/2)
Cell(x,y) = 0;
else
Cell(x,y) = 1;
}

Note this is unchecked, you may need to debug it and slightly change the if statement. But the idea is that you count the row your on (x) then check if the y element is greater then x (+ mirror it) so check if its less than count-x. You may not need the third && - but you can only do this for half of it, by doing x <= n/2 etc.

Hahaha I thought this was a linear algebra problem and you were doing matrix row ops to clear cells

Chris is right for the programming example if you just want to set the values to zero

Ok i get it. I didn't properly wrote the second condition. Thank you both for help.