How to draw tangent line at specified points in a curve
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I am having a an array of points x,y and respective angles at those specified points. I want to plot a tangent line at those points, i am unable to figure out how to proceed.
As shown in command window 1st column contains x points , 2nd column contains y points and 3rd column the respective tangent angle. Figure 1 is plot between x and y points. Thanking you.
Regards,
Mrinal
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Ngo Nguyen
2013-9-18
编辑:Ngo Nguyen
2013-9-18
If you have the coordinates M(x,y) , so you can find the slope m:
m= -(x - x0) / (y - y0) , (x0,y0) is the center of the circle
After that, you can plot the tangent line at M y = m*(x - x0) + y0 plot(x,y)
回答(1 个)
Image Analyst
2013-9-18
编辑:Image Analyst
2013-9-18
You have to figure out the slope at each point, then decide where the endpoints of the tangent line should be, then call line([x1, x2], [y1, y2], 'Color', 'b'). As a rough guess you can probably just say the slope at xn,yn is
slope = (y(n+1)-y(n-1)) / (x(n+1) - x(n-1));
or just get the slope from the tangent angle that you already have. Then the formula for the line is (from high school algebra)
y = slope * (x - x(n)) + y(n);
You just need to figure out how far away from x(n) do you want your endpoints of your tangent line segment. I believe you can just use xLeft = min(x) and xRight = max(x) if you just want the line to go everywhere and not see the endpoints lie inside the plot.
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