MATLAB绘制填充图（X轴上下两种颜色）

在实现X轴上下显示两种颜色的面积图或者填充图时，可以使用patch函数进行填充。这里主要的问题在于，需要先求解折线和X轴的交点。
这里选用1980-2020年的年平均Niño 3.4 SST Index绘制，参考代码和展示结果如下：

MATLAB代码如下：

%%
x = 1980 : 2020;
y = [0.14, -0.18, 0.91, 0.44, -0.72, -0.71, 0.08, 1.22, -1.01, -0.78, 0.17, 0.59, 0.62, 0.43, ...
    0.38, -0.02, -0.37, 1.19, 0.07, -1.09, -0.87, -0.33, 0.58, 0.23, 0.36, 0.03, 0.09, -0.56, ...
    -0.71, 0.35, -0.43, -0.84, -0.03, -0.22, 0.25, 1.47, 0.39, -0.20, 0.06, 0.53, -0.22];

figure(1);

colorstr = [0.4940 0.184 0.5560];
gc = get(gca);
set(gcf, 'position', [0, 50, 900, 600]);

set(gca, 'FontName', 'Arial', 'FontSize', FontSize1);
xlabel('X', 'FontSize', 24, 'FontName', 'Arial');
ylabel('Y', 'FontSize', 24, 'FontName', 'Arial');
hold on;

s = plot(x, y, 'k-');
s.LineWidth = 0.25;
hold on;

rr = axis;
s = plot(rr(1 : 2), [rr(4), rr(4)], 'k', [rr(2), rr(2)], rr(3 : 4), 'k');
hold on;

s = plot(rr(1 : 2), [0, 0], 'k');
s.LineWidth = 1.25;
hold on;

zeropts = [];
for pi = 1 : size(x, 2) - 1
    if y(pi) * y(pi + 1) >= 0
        continue;
    end    
    zeropts = [zeropts, x(pi) + abs(y(pi)) / (abs(y(pi)) + abs(y(pi + 1))) * (x(pi + 1) - x(pi))];
end

X = [x, zeropts];
Y = [y, zeropts - zeropts];

[Lat_all, I] = sort(X);
Slope_all = Y(I);

slope_ge0 = Slope_all(Slope_all >= 0);
lat_ge0 = Lat_all(Slope_all >= 0);

slope_le0 = Slope_all(Slope_all <= 0);
lat_le0 = Lat_all(Slope_all <= 0);

patch([lat_ge0'; flipud(lat_ge0')], ...
    [min(slope_ge0' - slope_ge0', slope_ge0'); flipud(max(slope_ge0' - slope_ge0', slope_ge0'))], ...
    'r', 'FaceA', 0.55, 'EdgeA', 0);
hold on;

patch([lat_le0'; flipud(lat_le0')], ...
    [min(slope_le0' - slope_le0', slope_le0'); flipud(max(slope_le0' - slope_le0', slope_le0'))], ...
    'b', 'FaceA', 0.55, 'EdgeA', 0);
hold on;

s = plot(x, y, 'k-');
s.LineWidth = 1.25;
hold on;

rr = axis;
s = plot(rr(1 : 2), [0, 0], 'k');
s.LineWidth = 1.25;
hold on;

plot(rr(1:2), [rr(4), rr(4)], 'k-', [rr(2), rr(2)], rr(3:4), 'k-');
hold on;