Matlab-如何在曲线上绘制切线 [英] Matlab - how to draw tangent on curve

问题描述

我在matlab中用以下方式绘制了一个图形:

I have plotted a graph in matlab with:

plot(x,y)

我的图具有不同的斜率，如何在每个斜率上绘制切线并计算斜率的系数?

and my graph has different slopes, how do i draw tangents on each slope and calculate the coefficient for the slope?

推荐答案

如果绘制点没有明确的功能，则可以使用

If you don't have an explicit function for the plotted points, you can use finite differences for estimating the derivative. The following is appropriate for points not on the border of the data span:

plot(x,y);
hold all;

% first sort the points, so x is monotonically rising
[x, sortidx] = sort(x);
y = y(sortidx);

% this is the x point for which you want to compute the slope
xslope = (x(1)+x(end))/2;

idx_a = find(x<xslope,1,'last');
idx_b = find(x>xslope,1,'first');
% or even simpler:
idx_b = idx_a+1;
% this assumes min(x)<xslope<max(x)

xa = x(idx_a);
xb = x(idx_b);
slope = (y(idx_b) - y(idx_a))/(xb - xa);

现在绘制该斜率，取决于您想要的内容:仅需短线:

Now drawing that slope, it depends on what you want: just a short line:

yslope = interp1(x,y,xslope);
ya_sloped = yslope + (xa-xslope)*slope;
yb_sloped = yslope + (xb-xslope)*slope;
line([xa;xb],[ya_sloped;yb_sloped]);

或更长的行

yslope = interp1(x,y,xslope);
xa = xa + 4*(xa-xslope);
xb = xb + 4*(xb-xslope);
ya_sloped = yslope + (xa-xslope)*slope;
yb_sloped = yslope + (xb-xslope)*slope;
line([xa;xb],[ya_sloped;yb_sloped]);

我很确定这段代码中没有错误，但是当我有matlab时，我会对其进行测试；)

I'm pretty sure there're no bugs in this code, but I'll test it out when I have matlab around ;)

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