小白一枚，请大佬别嘲笑
为什么我用MATLAB绘制相关系数矩阵的时候得到的图像全部是蓝色或者大部分是蓝色呢
%% 相关系数法
covmat = corrcoef(hs300);
varargin = {'x1','x2','x3','x4','x5','x6','x7','x8','x9','x10','x11','x12','x13','x14','x15','x16','x17','x18' 'y'};
figure;
x = size(covmat, 2);
imagesc(covmat);
set(gca,'XTick',1:x);
set(gca,'YTick',1:x);
% if nargin > 1
    set(gca,'XTickLabel',varargin);
    set(gca,'YTickLabel',varargin);
% end
axis([0 x+1 0 x+1]);
grid;
colorbar;