matlab - 使用 MatLab 在参数曲线上绘制切线

Question

这个问题与这个问题非常相似，但在这里我有参数方程，例如：

x = sin(t)

y = cos(t)

如何在特定点（该点由用户选择）的参数曲线上绘制切线？

任何想法，将不胜感激。

Answer 1

这个答案从Rody Oldenhuis 的不错的一个（你链接到）中撕掉了代码。它只修改绘图例程以保持选定的点和切线连接到圆。正如评论员所指出的，其余的只是几何：

function test

hh = figure(1); clf, hold on
grid on

x = [0:0.01:2*pi]';
f = @(x) sin(x);
g = @(x) cos(x);
fprime = @(x,y) -x./y;
circle = [f(x) g(x)];

plot(g(x), f(x), 'r')
axis tight

D = [];
L = [];
set(hh, ...
    'WindowButtonMotionFcn', @mouseMove,...
    'WindowButtonDownFcn', @mouseClick);


    function mouseMove(varargin)

        coords = get(gca, 'currentpoint');
        xC = coords(1,1);
        yC = coords(1,2);

        % find nearest point on the circle
        [minr2 imin]=min(sum((circle - ones(size(circle,1),1)*coords(1,1:2)).^2,2));


        if ishandle(D)
            delete(D);
        end
        D = plot(circle(imin,1), circle(imin,2), 'ko');

    end

    function mouseClick(obj, varargin)

        switch get(obj, 'selectiontype')

            % actions for left mouse button
            case 'normal'

                coords = get(gca, 'currentpoint');
                xC = coords(1,1);
                yC = coords(1,2);

                % find nearest point on the circle
                [minr2 imin]=min(sum((circle - ones(size(circle,1),1)*coords(1,1:2)).^2,2));

                xC=circle(imin,1);
                yC=circle(imin,2);

                m  = fprime(xC,yC);
                b  = yC-m*xC;

                if ishandle(L)
                    delete(L);
                end

                L = line(xC+[-pi/2;pi/2], m*(xC+[-pi/2;pi/2])+b);

            case 'alt'
                % actions for right mouse button

            case 'extend'
                % actions for middle mouse button

            case 'open'
                % actions for double click

            otherwise
                % actions for some other X-mouse-whatever button

        end

    end

end