# How to plot a marked point in a graph and connect it with other points?

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Vishnuvardhan Naidu Tanga on 14 Oct 2021
Commented: Mathieu NOE on 15 Oct 2021
Hello all,
I am trying to mark a specific point in the plot and need to connect it with other points. I have tried using plot(x_pos, y_pos) but i am getting an error. I have marked the points in the excel data. I am also attaching a demo plot on what i required. Please kindly help me. Thanks in advance.
My code:
data = table2array(Z) ;
N = size(data,2);
Nsp = N/2;
ttlc = {'x=10mm', 'x=250mm', 'x=500mm', 'x=1000mm', 'x=1500mm'};
xofst = [10 250 500 1000 1500];
figure
ylim([-1 1]*250)
xlim([0 1750])
hold on
for k = 1:Nsp
col = [2 1]+2*(k-1);
famp = 5;
datacol1 = data(:,col(1))*famp+xofst(k);
hp(k) = plot(datacol1, data(:,col(2)), 'LineWidth',2);
minx(k) = min(datacol1);
maxx(k) = max(datacol1);
plot([1;1]*[minx(k) maxx(k)], ([1;1]*ylim).', ':k', 'LineWidth',1)
plot([minx(1) maxx(1)]-minx(1)+minx(k), [0 0], '-k', 'LineWidth',1)
Line_Coordinates = [minx(1) maxx(1)]-minx(1)+minx(k);
LineLength = diff(Line_Coordinates);
end
hold off
hl = legend([hp], ttlc, 'Location','northeastoutside'); Mathieu NOE on 14 Oct 2021
hello
this is a first attempt
the outer lines was fairly easy to plot
the two inner lines , it's a bit coded just to show a principle but there is yet no "scientific" method to pick the points . Now this is where you need to tell more about how to choose the inner points
so far this is where I am : data = table2array(Z) ;
N = size(data,2);
Nsp = N/2;
ttlc = {'x=10mm', 'x=250mm', 'x=500mm', 'x=1000mm', 'x=1500mm'};
xofst = [10 250 500 1000 1500];
figure(1)
ylim([-1 1]*250)
xlim([0 1750])
hold on
for k = 1:Nsp
col = [2 1]+2*(k-1);
famp = 5;
datacol1 = data(:,col(1))*famp+xofst(k);
datacol2 = data(:,col(2));
minx(k) = min(datacol1);
maxx(k) = max(datacol1);
miny(k) = min(datacol2);
maxy(k) = max(datacol2);
%%%%%%%%%%%%%%%%%%%%% special code for inner line %%%%%%%%%%%%%%%%%%%%%
ll = length(datacol1);
ind1 = round(ll/(3.5+0.5*k));
ind2 = ll - round(ll/(2.5+0.5*k));
y_pos(k) = datacol2(ind1);
y_neg(k) = datacol2(ind2);
x_pos(k) = datacol1(ind1);
x_neg(k) = datacol1(ind2);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
hp(k) = plot(datacol1, datacol2, 'LineWidth',2);
plot([1;1]*[minx(k) maxx(k)], ([1;1]*ylim).', ':k', 'LineWidth',1)
plot([minx(1) maxx(1)]-minx(1)+minx(k), [0 0], '-k', 'LineWidth',1)
Line_Coordinates = [minx(1) maxx(1)]-minx(1)+minx(k);
LineLength = diff(Line_Coordinates);
end
plot(minx,miny,'dr',minx,maxy,'db')
plot(minx,miny,'r',minx,maxy,'b')
plot(x_pos,y_pos,'dr',x_neg,y_neg,'db')
plot(x_pos,y_pos,'--r',x_neg,y_neg,'--b')
hold off
hl = legend([hp], ttlc, 'Location','northeastoutside');
Mathieu NOE on 15 Oct 2021
My pleasure
Have a nice weekend.too !