Plot questions (variables at legend, labeling a marker)

hi , so i got two questions. i made a function to find an intersection between two lines (y=x+c) and then plots the lines. Now i have two questions, 1)how do i make the leggend accept the input variables to display. 2) how do i label the intersection point on the plot itself?

function p=inters(v1,v2) %v1,v2 are lines inputed as vectors i.e v1=[2 -1] v2=[-3,1] (y=2x-1,y=-3x+1)
xt=v1(1)-(v2(1));
c=v1(2)-(v2(2));
x0=(-c)/xt;
y0=v1(1)*x0+v1(2);
p=[x0,y0];
x=x0-5:x0+5;
xmarkers=x0;
ymarkers=y0;
plot(x,polyval(v1,x),'b',xmarkers,ymarkers,'b*')
hold
plot(x,polyval(v2,x),'g')

i need the legend to change depending on the input to the fuction v1 and v2 so me typing legend y=2x-1 wont work...

Answer 1

[Star Strider]

To label the intersection, use the text function, for example:

text(x0+0.1, y0+0.1, sprintf('Intersection at (%.3f, %.3f)', x0, y0))

Do something similar with the legend text:

lgndtxt1 = sprintf('y = %.3f X %+.3f', v1);
lgndtxt2 = sprintf('y = %.3f X %+.3f', v2);
legend(lgndtxt1, lgndtxt2, 'Location', 'NE')

You will have to experiment with this to get the result you want.

[Alex]

this works well exept the part where it legends my marker instead of the second line. any way for it to ignore markers in legend ?

[Star Strider]

The easiest way to do that is to simply rearrange the plot statements and not have a legend entry for the markers.

The last few lines of your code then become:

. . .
xmarkers=x0;
ymarkers=y0;
plot(x,polyval(v1,x),'b')
hold
plot(x,polyval(v2,x),'g')
plot(xmarkers,ymarkers,'b*')

lgndtxt1 = sprintf('y = %.3f X %+.3f', v1);
lgndtxt2 = sprintf('y = %.3f X %+.3f', v2);
legend(lgndtxt1, lgndtxt2, 'Location', 'NE')