srcnn中的x3.mat是什么

%% set parameters

 up_scale = 3;

 model = 'model\9-5-5(ImageNet)\x3.mat';

% up_scale = 3;% model = 'model\9-3-5(ImageNet)\x3.mat';

% up_scale = 3;% model = 'model\9-1-5(91 images)\x3.mat';

% up_scale = 2;% model = 'model\9-5-5(ImageNet)\x2.mat'; 

% up_scale = 4;% model = 'model\9-5-5(ImageNet)\x4.mat';