% Get signal and variance from sqw object, and a logical array of which values to ignore
% 
%   >> [s,var,mask_null] = sigvar_get (w)
%%   Overloaded methods:
%      sqw/sigvar_get
%      IX_dataset_3d/sigvar_get
%      IX_dataset_2d/sigvar_get
%      IX_dataset_1d/sigvar_get
%      sqw/sigvar_get
%      d4d/sigvar_get
%      d3d/sigvar_get
%      d2d/sigvar_get
%      d1d/sigvar_get
%      d0d/sigvar_get
%