如何繪製一條曲線的兩個斜率

Question

我在Matlab中有一條曲線。我想繪製兩個斜坡;第一個斜坡是1,2,3和4點。第二個斜坡是繪製其餘點。見圖：

Answer 1

當你說「暗算兩個斜坡」，我會認爲你的意思是你要繪製最能接近您的數據的兩個部分的線。爲此，您需要執行曲線擬合程序，如最小二乘法。有關MATLAB中最小二乘逼近的更多信息，請參閱此問題：How do I use the least squares approximation in MATLAB?

我將假設您的數據存儲在矢量x和y中。

%//number of points for the first part of the curve: 
n=4; 

%// Separate (x,y) into (x1,y1) and (x2,y2) 
x1 = x(1:n); x2=x(n+1:end); 
y1 = y(1:n); y2=y(n+1:end); 

%// fit a line y=A1*x+A2 to the first set of points: 
M=[x1(:) ones(length(x1),1)]; 
A = M\y1(:); %//A(1) is your slope, A(2) is your y-intercept 

%// fit a line y=B1*x+B2 to the second set of points: 
M=[x2(:) ones(length(x2),1)]; 
B = M\y2(:); %//B(1) is your slope, B(2) is your y-intercept 

%//Plot: 
hold on 
fplot(@(x)A(1)*x+A(2),[min(x1) max(x1)]) 
fplot(@(x)B(1)*x+B(2),[min(x2) max(x2)])