Mercurial > repos > public > sbplib
view minors.m @ 577:e45c9b56d50d feature/grids
Add an Empty grid class
The need turned up for the flexural code when we may or may not have a grid for the open water and want to plot that solution.
In case there is no open water we need an empty grid to plot the empty gridfunction against to avoid errors.
author | Jonatan Werpers <jonatan@werpers.com> |
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date | Thu, 07 Sep 2017 09:16:12 +0200 |
parents | eaf557023fbe |
children |
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function [minor, sub] = minors(A, verbose) default_arg('verbose', true); [n, m] = size(A); if n ~= m error('A must be square'); end sub = {}; ks = {}; ind = 1:n; for k = 1:n C = nchoosek(ind,k); for i = 1:size(C,1) ks{end + 1} = k; sub{end + 1} = A(C(i,:),C(i,:)); end end for i = 1:length(sub) if verbose fprintf('%d:\n', ks{i}); disp(sub{i}) end minor(i) = det(sub{i}); end end % A is positive semidefinite if all minors are non-negative % A is negative semidefinite if all odd minors are non-positive and all even minors are non-negative