Mr. Roman Pearce

## 1683 Reputation

19 years, 203 days
CECM/SFU
Research Associate

I am a research associate at Simon Fraser University and a member of the Computer Algebra Group at the CECM.

## Sparse Matrix-Vector product using evalu...

Maple

This tip comes care of Dr. Michael Monagan at Simon Fraser University. Represent your sparse matrix as a list of rows, and represent each row as a linear equation in an indexed name. For example:

A := [[1,0,3],[2,0,0],[0,4,5]];

S := [ 1*x[1] + 3*x[3], 2*x[1], 4*x[2]+5*x[3] ];

To compute the product of the matrix A with a Vector X, assign x[i] := V[i] and evaluate. This can be done inside of a procedure because x is a table.

V := [7,8,9]: for i to 3 do x[i...

## Sparse Transpose...

Maple

This is a quick programming exercise to correct the following problem in Maple:

for n from 8 to 12 do
A := Matrix(2^n, 2^n, storage='sparse'):  # zero matrix
print( 2^n, time(LinearAlgebra:-Transpose(A)) );
end do:

The problem is that the LinearAlgebra:-Transpose command is not sparse. That is, the time it takes is proportional to the overall size of the matrix and not to the number of non-zero entries - even when your matrix uses sparse storage. In this post we will look at what is required to program a new Transpose command which can handle much larger matrices.

## MaplePrimes beta...

How long is MaplePrimes going to remain in beta ? Are there more features planned, or are you just waiting for a more appropriate time to make an announcement ? Personally, I think it's done, and overall it's a very good job. By the way, I hope the company makes a good effort to promote this site at the conference. Set up a computer set up in the main lobby where people could see the site. Just use a notebook with external keyboard, monitor, and mouse, and mooch wireless internet from the venue. On a sidenote, I think wireless internet was probably the most requested feature of last year's conference.

## Can we please increase the time for logi...

Can we please increase the amount of time uses are logged in after entering their name and password ? I have lost a number of good posts because the time expires while I am writing the post and then I hit submit. You get a blank screen telling you to log in and there is no way to use the forward and back buttons on your browser to resubmit the post. Usually I copy and paste my post to avoid this problem, however sometimes I forget and it's a terrible waste.

## Generating Random Linear Polynomials...

Lately I have been experimenting with structured Gaussian elimination. This is a technique for reducing large sparse systems of linear equations to much smaller dense ones, which can then be solved using a modular method. Needless to say, I had to generate some large sparse linear systems. I wanted the equations to be written as polynomials, because that is the natural sparse representation in Maple and it makes programming structured Gaussian elimination easier (you can use has and indets, for example). So I tried my favorite randpoly command. This was me trying to generate one linear equation:
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