What's New (Decemeber 2005)

(1) New texi documentation; courtesy of Robert Dodier.

(2) Added function mat_fullunblocker; a fully recursive version of
mat_unblocker.

(3) Added function mat_trace; a block matrix friendly function for
the matrix trace.

(4) Improved algorithm for matrix condition number estimation.

The new version of linalg can be downloaded from 
http://www.unk.edu/facstaff/profiles/willisb/.

A tour of new functions:

(1) The file linearalgebra/conjugate.lisp has an alternative to 
the /eigen/conjugate function.  The /eigen/conjugate function
only does the substitution %i --> -%i.  The conjugate
function in linearalgebra is (I hope) somewhat smarter.

(%o1) c:/maxima/linearalgebra/linalg.mac
(%i2) declare(z,complex)$
(%i3) conjugate([z,z^2,sqrt(z)]);
(%o3) [conjugate(z),conjugate(z)^2,conjugate(sqrt(z))]

Off the branch cut of sqrt, conjugate and sqrt commute. Telling
Maxima that z isn't on branch cut allows it to transform
conjugate(sqrt(z)) --> sqrt(conjugate(z)).

(%i4) assume(imagpart(z) > 0)$
(%i5) conjugate(sqrt(z));
(%o5) sqrt(conjugate(z))

(2) New functions for generating matrices:

(%i6) hilbert_matrix(2);
(%o6) matrix([1,1/2],[1/2,1/3])
(%i7) vandermonde_matrix([a,b]);
(%o7) matrix([1,a],[1,b])

(3) A matrix kronecker_product

(%i9) kronecker_product(hilbert_matrix(2), vandermonde_matrix([5,6]));
(%o9) matrix([1,5,1/2,5/2],[1,6,1/2,3],[1/2,5/2,1/3,5/3],[1/2,3,1/3,2])

(4) A function that converts block matrices to unblocked matrices

(%i12) matrix([matrix([4,5]), matrix([6,7])]);
(%o12) matrix([matrix([4,5]),matrix([6,7])])
(%i13) mat_unblocker(%);
(%o13) matrix([4,5,6,7])

(5) LU factorization

There is code for LU factorization.  It uses partial pivoting when
the matrix is numeric.

(%i1) load("linalg");
Warning - you are redefining the Maxima function RANK
(%o1) c:/maxima/linearalgebra/linalg.mac
(%i2) lu_factor(matrix([a,b],[c,d]));
(%o2) [matrix([a,b],[c/a,d-(b*c)/a]),[1,2]]

Do the LU factorization using CRE expressions.  Try this using
the general representation -- it is very slow.

(%i4) lu_factor(vandermonde_matrix([a,b,c,d,e]),crefield)$
(%i5) m : first(%)$
(%i6) factor(product(m[i,i],i,1,5));
(%o6) (b-a)*(c-a)*(c-b)*(d-a)*(d-b)*(d-c)*(e-a)*(e-b)*(e-c)*(e-d)

LU factor using CL complex numbers 

(%i14) w[i,j] := ?random(1.0) + %i * ?random(1.0)$
Evaluation took 0.00 seconds (0.00 elapsed)
(%i15) m : genmatrix(w,100,100)$
Evaluation took 0.45 seconds (0.45 elapsed)
(%i16) lu_factor(m,complexfloatfield)$
Evaluation took 1.73 seconds (1.73 elapsed)

(This code will not win any speed awards.)

There is also code for solving linear systems using the LU
factorization

(%i19) m : hilbert_matrix(5)$
(%i20) m : lu_factor(m)$
(%i21) lu_backsub(m, matrix([1],[1],[1],[1],[1]));
(%o21) matrix([5],[-120],[630],[-1120],[630])
(%i22) hilbert_matrix(5) . %;
(%o22) matrix([1],[1],[1],[1],[1])

(6) My spectral representation code is now included in linalg.

As always, let me know how I can improve this code.

Barton Willis