highlighting a sections in a plot using patch

Question

ran 2023-9-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2019801-highlighting-a-sections-in-a-plot-using-patch

移动：Dyuman Joshi 2023-9-12

i have the following code and i get the result as shown in the image. I eant to shade all the way dwon to the line what i do wrong?

% Fit the lowess curve
ywf =fitresultLow(sort(xw));
% Determine where the function goes up and where it goes down
up_indices = find(diff(ywf) > 0);
down_indices = find(diff(ywf) < 0);
% Calculate regions where ywf is above a threshold (0.5 in this example)
threshold = 0.5;
up_regions = [];
down_regions = [];
if ~isempty(up_indices)
    up_regions = [up_indices(1)]; % Initialize with the first up index
    for i = 2:length(up_indices)
        if up_indices(i) > up_indices(i-1) + 1
            up_regions = [up_regions, up_indices(i)];
        end
    end
end
if ~isempty(down_indices)
    down_regions = [down_indices(1)]; % Initialize with the first down index
    for i = 2:length(down_indices)
        if down_indices(i) > down_indices(i-1) + 1
            down_regions = [down_regions, down_indices(i)];
        end
    end
end
% Sort regions and create shading
regions = sort([up_regions, down_regions]);
xw1 = sort(xw);
lower_y_coordinate = min(Nu);
figure;
plot(xw1, Nu);
hold on;
for k = 1:2:length(regions) - 1
    xrng = regions(k):regions(k + 1);
    patch([xw1(xrng), flip(xw1(xrng))], [Nu(xrng)' ones(size(Nu(xrng)')) * lower_y_coordinate], 'r', 'FaceAlpha', 0.5);
end
% Create a polygon to extend shading all the way down
fill([xw1(1), xw1(end), xw1(end), xw1(1)], [lower_y_coordinate, lower_y_coordinate, lower_y_coordinate, lower_y_coordinate], 'r', 'FaceAlpha', 0.5);
hold off;
grid on;