NCminBall

description:

[opt,g,decom_sohs,decom_ball,base,SDP_data,Z_dual,H,Hshift] = NCminBall(f,params) computes the minimum opt of the polynomial f on an nc ball.

It solves:

    min <L_f,H>

    H ... hankel (moment) matrix

    H(1) = 1

    H >= 0

    H_shift >= 0

    (H_shift)_p,q = L(p^*(1-\sum_ix_i^2)q)

  WHICH is dual to:

    sup eps

    s.t. f-eps = SOHS + \sum_i h_j^*(1-\sum_i x_i^2)h_j

arguments:

f is an NCpoly representing a polynomial.

With params.precision we can set the smallest value that is considered to be nonzero in numerical calculations; if the command is called without it, we assume the precision set with the command NCsetPrecision or the value set in NCparam.m.

params.messages is used to optionally turn on (1) and off (0) verbose output; default value is 1 (on).

params.solver sets the solver to be used for SDP and overrides the value set in the global option file NCparam.m. (currently SeDuMi, SDPA-M or SDPT3 are supported) 

params.eps sets the desired accuracy iy you are using SeDuMi as SDP solver. Setting params.eps=0 lets SeDuMi run as long as it can make progress.

params.justSDP_data == 1 means that the program ends when the SDP_data is prepared and nothing else is computed. It is optional; the default value is 0.

params.decomposition == 0 means that no SOHS decomposition over an nc ball will actually be computed. It is optional; the default value is 1.

params.module_up == 0 means that search for the decomposition is within quadratic module of degree d_max and params.module_up == 1 means module of degree d_max+2; the default value is 0.

output:

opt ... optimal value of the SDP

g ... represents an nc ball

decom_sohs ... sohs part of the sohs decomposition over nc ball

decom_ball ... weighted part of the sohs decomposition over nc ball

base ... is a list of monomials which appear in the SOHS decomposition over nc ball

SDP_data ... is a structure holding all the data used in SDP solver

Z_dual ... dual solution

H ... Hankel matrix

Hshift ... shifted Hankel matrix

possible usage:

NCminBall(f), NCminBall(f,params)