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%直线与直线相交
function [X,Y]=pll(X1,Y1,X2,Y2)
% 直线相交求交点
A1=Y1(1)-Y1(2);
B1=X1(2)-X1(1);
C1=Y1(2)*X1(1)-Y1(1)*X1(2);
A2=Y2(1)-Y2(2);
B2=X2(2)-X2(1);
C2=Y2(2)*X2(1)-Y2(1)*X2(2);
D=det([A1,B1;A2,B2]);
X=det([-C1 B1;-C2 B2])/D;
Y=det([A1 -C1;A2,-C2])/D;
调用格式：
x1=[1 5];y1=[1 5];x2=[1 5];y2=[5,1];
[x,y]=pll(x1,y1,x2,y2);
plot(x1,y1,'r');
hold on
plot(x2,y2,'b');
plot(x,y,'ko');
直线与多条直线相交
xi=[1 2 3 4 5];yi=[2 6 3 6 1];
plot(xi,yi);hold on
x1=[1 5];y1=[4 5];line(x1,y1);
x=zeros(size(xi));
y=x;
for i=1:5-1
x2=xi([i i+1]);y2=yi([i i+1]);
[x,y]=pll(x1,y1,x2,y2);
plot(x,y,'ro')
end
%直线与曲线相交
x=-8:0.1:8;y=x;[X,Y]=meshgrid(x,y);
R=sqrt(X.^2+Y.^2)+eps;Z=sin(R)./R;
contour(Z,3);hold on
c=contour(Z,3);
x=[0 360];y=[0 400];
y=(y(2)-y(1))/(x(2)-x(1))*(x-x(1))+y(1);z=[0 0];
line(x,y,z);c=c';
X=c(:,1);Y=c(:,2);
r0=abs(Y-(y(2)-y(1))/(x(2)-x(1))*(X-x(1))+y(1))<=0.5; zz=0;yy=r0.*Y;xx=r0.*X;
plot(xx(r0~=0),yy(r0~=0),'ro')
%曲线与曲线相交
x=0:pi/400:2*pi;