Matlab雙色圖

Question

我想畫一個函數f給出2個向量：x和y，所以y=f(x)。 我用plot(x,y)，但現在我需要它是藍大於0和紅色下所以它看起來像這樣：

Answer 1

當您繪製在MATLAB中的向量，是充滿NaN的是矢量的任何部分將不會被繪製。因此，實現您的目標的一個訣竅就是在原始頂點上繪製第二行，並使用Nans移除相關的片段。例如，

x = linspace(1,100,1000); 
y = sin(x); 

% Using a cutoff of y>=0.5 
belowCutoff  = y; 
belowCutoff(y>=0) = NaN; % Replace points above cutoff with NaNs; 

figure; 
plot(x,y,'r',x, belowCutoff, 'b'); 

Answer 2

y0 = 0; % threshold 
color1 = [1 0 0]; % below threshold 
color2 = [0 0 1]; % above threshold 
x = 1 : 10; 
y = randn(1, 10); 
threshold_plot(x, y, y0, color1, color2); 

---

function threshold_plot(x, y, y0, color1, color2) 
hold on; 
n = length(x); 
for i = 2 : n 
    x1 = x(i - 1); y1 = y(i - 1); 
    x2 = x(i); y2 = y(i); 
    ascending = y1 < y2; 
    if x1 == x2 
    if ascending 
     plot([x1 x2], [y1, y0], 'Color', color1); 
     plot([x1 x2], [y0, y2], 'Color', color2); 
    else 
     plot([x1 x2], [y1, y0], 'Color', color2); 
     plot([x1 x2], [y0, y2], 'Color', color1); 
    end; 
    elseif y1 == y2 
    if threshold <= y1 
     plot([x1 x2], [y1 y2], 'Color', color2); 
    else 
     plot([x1 x2], [y1 y2], 'Color', color1); 
    end; 
    else 
    a = (y2 - y1)/(x2 - x1); 
    b = y1 - a * x1; 
    x0 = (y0 - b)/a; 
    if x1 <= x0 && x0 <= x2 
     if ascending 
     plot([x1 x0], [y1, y0], 'Color', color1); 
     plot([x0 x2], [y0, y2], 'Color', color2); 
     else 
     plot([x1 x0], [y1, y0], 'Color', color2); 
     plot([x0 x2], [y0, y2], 'Color', color1); 
     end; 
    else 
     if y0 <= y1 
     plot([x1 x2], [y1 y2], 'Color', color2); 
     else 
     plot([x1 x2], [y1 y2], 'Color', color1); 
     end; 
    end; 
    end; 
end;