MATLAB: To find intersection point of two lines

curve fittingdigital image processingmatrix

      x1=7.8;
      x2=8.5;
      y1=0.96;
      y2=0.94;
      p1 = polyfit([x1 x2], [y1 y2], 2);
      b1= polyval(p1,1);
      m1=polyval(p1,2)-b1;
      x3=8.25;
      x4=8.25;
      y3=0;
      y4=.99;
      p2 = polyfit([x3 x4], [y3 y4], 2);
      b2 = polyval(p2, 1);
      m2 = polyval(p2, 2) - b2;
I got x value = -1.2867; from which co-ordinate this value corresponds to? Actually I want to compute intersection of two line with respect to x=[7.8 8.25 8.5]; y=[0.96 0.99 0.94]; over which those two lines are plotted?
x=[7.8 8.25 8.5];
y=[0.96 0.99 0.94];
p=polyfit(x,y,2);
f=polyval(p,x);
plot(x,y,'o',x,f,'-');
hold on;
line([7.8 8.5],[0.96 0.94]);
hold on;
line([8.25 8.25],[0 0.99]);

Best Answer

Hi,
not sure if I understand correctly what you want but is this what you are looking for?
%line1
x1  = [7.8 8.5];
y1  = [0.96 0.94];
%line2
x2 = [8.25 8.25];
y2 = [0 0.99];
%fit linear polynomial
p1 = polyfit(x1,y1,1);
p2 = polyfit(x2,y2,1);
%calculate intersection
x_intersect = fzero(@(x) polyval(p1-p2,x),3);
y_intersect = polyval(p1,x_intersect);
line(x1,y1);
hold on;
line(x2,y2);
plot(x_intersect,y_intersect,'r*')
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