NCSOStoolsdemo - Basics of toolbox for symbolic computation with polynomials in noncommuting variables

%**************************************************************************

% Toolbox for symbolic computation with polynomials in noncommuting       *

% variables                                                               *

%**************************************************************************

% -------------------------------------------------------------------------

% First we construct some symbolic noncommuting variables.

% -------------------------------------------------------------------------

>> NCvars x y z

% -------------------------------------------------------------------------

% Now we can define some polynomials in noncommuting variables.

% -------------------------------------------------------------------------

>> f = x^2 + 5*x*y - y*z + 3*x*y*z;

>> g = 2*y*z - z^2;

% -------------------------------------------------------------------------

% All basic arithmetic operations are defined in standard way.

% -------------------------------------------------------------------------

>> f + g, f - g, f*g, -f, g^2, g'

ans = x^2+5*x*y+3*x*y*z+y*z-z^2

ans = x^2+5*x*y+3*x*y*z-3*y*z+z^2

ans = 2*x^2*y*z-x^2*z^2+10*x*y^2*z+6*x*y*z*y*z-5*x*y*z^2-3*x*y*z^3-2*y*z*y*z+y*z^3

ans = -x^2-5*x*y-3*x*y*z+y*z

ans = 4*y*z*y*z-2*y*z^3-2*z^2*y*z+z^4

ans = 2*z*y-z^2

% -------------------------------------------------------------------------

% We can also define matrices of such polynomials.

% -------------------------------------------------------------------------

>> A = [2*x*y, x]

A = 2*x*y   x

>> B = [x*y + x, y; y^2, x - y]

B = x+x*y     y

      y^2   x-y

% -------------------------------------------------------------------------

% All basic operations on such matrices are defined.

% -------------------------------------------------------------------------

>> A*B, B*B, B.*B, A', trace(B), diag(B), triu(B), [A; sum(B)]

ans = 2*x*y*x+2*x*y*x*y+x*y^2   x^2-x*y+2*x*y^2

ans = x^2+x^2*y+x*y*x+x*y*x*y+y^3     x*y+x*y^2+y*x-y^2

          x*y^2+y^2*x+y^2*x*y-y^3   x^2-x*y-y*x+y^2+y^3

ans = x^2+x^2*y+x*y*x+x*y*x*y               y^2

                          y^4   x^2-x*y-y*x+y^2

ans = 2*y*x

          x

ans = 2*x+x*y-y

ans =  x+x*y

         x-y

ans = x+x*y     y

          0   x-y

ans =     2*x*y   x

      x+x*y+y^2   x

% -------------------------------------------------------------------------

% We can also do symbolic (in)equality test.

% -------------------------------------------------------------------------

>> B

B = x+x*y     y

      y^2   x-y

>> B + diag(diag(B)) == tril(B) + triu(B)

ans = 1     1

      1     1

>> B ~= B'

ans = 1     0

      1     0

% -------------------------------------------------------------------------

% We can evaluates a polynomial with substitutions and write monomials

% shortly using exponents or in expanded form without using exponents

% regardless of the parameter NC_using_exponents set in NCparam.m.

% -------------------------------------------------------------------------

>> f

f = x^2+5*x*y+3*x*y*z-y*z

>> NCeval(f,{{x,x+y},{y,x-y},{z,0}})

ans = 6*x^2-4*x*y+6*y*x-4*y^2

>> NCexpand(ans)

ans = 6*x*x-4*x*y+6*y*x-4*y*y

>> NCsimplify(ans)

ans = 6*x^2-4*x*y+6*y*x-4*y^2