Message Boards Message Boards

Visualizing matrix reduction to reduced echelon and LU forms step-by-step: do such exist?

Yesterday I saw a presentation by Cleve Moler, of MathWorks, that used M****b to create a visual transformation of a square matrix to its LU decompostion (along with permuation vector from the partial pivoting). It showed each step of the process, one by one.

Are there similar visualizations, done with Mathematica, for:

(1) Step-by-step transfromation of any given (possibly non-square) matrix to its reduced echelon form?

(2) Step-by-step transormation of any given square matrix into its LU decomposition?

By "visualization" here I do not refer to any geometric realization, just highlighting at each step the entry or entries involved and the row or rows involved and then showing the changed matrix after that step.

Moler's visualization was done, of course, with M****b, but he created it by producing scores of individual snapshots of the matrix appearance at each step and then by showing those snapshots as a discrete-time animation in Power Point.

With Mathematica, such visualization should e much easier to present, using Manipulate or, if necessary, Dynamic directly.

I don't want to "reinvent the wheel," hence this quetion.

POSTED BY: Murray Eisenberg
4 Replies
Posted 6 months ago

The work by "Nasser" is nice, but it outputs the whole process as one long result. What I want is a Manipulate (or a Dynamic) with a button such that, each time one presses it, the next elementary operation is performed and the then-current state is shown. Another version of such a program would require the user to provide input specifying the next operation at each step.

Perhaps Nasser's code is adaptable to do that.

Otherwise, I can go back to an RREF function I wrote some 25 years ago -- my version of a function that my sophomore linear algebra students were tasked to develop over the course of several weeks, starting with little functions to swap two specified rows, to add a specified multiple of one specified row to another specified row, and then to put these together into a controllng program to do the whole RREF iteratively. "All" that would be needed would be to stop after each step and show the elementary operaty (or elementary matrix) used and thethen-current state of the matrix.

POSTED BY: Updating Name

There is this Demonstration.

https://demonstrations.wolfram.com/LUDecomposition/

And this Wolfram U course. https://www.wolfram.com/broadcast/video.php?c=105&p=30&ob=title&o=ASC&v=3327

But maybe one can modify the row reduction step-my-step methods to do LU. The problem (as you are aware) isn't that more work is needed, but rather than LU actually does less than full row reduction. So modifications would be needed to quell the ardor of row reduction in key places.

POSTED BY: Daniel Lichtblau

Thank you for those citations! (Awkward to search just within Demonstrations or just within community.wolffram.com --- I do wish each would provide an option to so constrain searches and thereby avoid "site:..." specifier in Google, say.

What about LU-decomposition step-by-step?

POSTED BY: Murray Eisenberg
Reply to this discussion
Community posts can be styled and formatted using the Markdown syntax.
Reply Preview
Attachments
Remove
or Discard

Group Abstract Group Abstract