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

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:

Z = readtable('Atq100.xlsx') ;
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');

Answer 1

[Mathieu NOE]

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 :

Z = readtable('Atq100.xlsx') ;
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');

[Vishnuvardhan Naidu Tanga]

Hello @Mathieu NOE,

Thank you for the response. I have selected the points on basis of the highest y value/2, which gives me some value and i am looking for the nearest value in the same y data and i need to plot it.

For example:

The highest vale in Y1 colume is 40.075/2 (cell B59 ) gives me a result 20.0375. The nearest corresponding values are in cells B16 and B117. I need to plot this point. Simiarly for the other y data. I hope you can understand what I need.

[Mathieu NOE]

hello again

ok got it

this is the revised code and result

clc
clearvars
close all

Z = readtable('Atq100.xlsx') ;
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) = maxy(k)/2; % initial guess
            % find nearest value
            [~,ind_pos] = min(abs(datacol2-y_pos(k)));
            y_pos(k) = datacol2(ind_pos); % final value
            x_pos(k) = datacol1(ind_pos); % final value
            
        y_neg(k) = miny(k)/2; % initial guess
            % find nearest value
            [~,ind_neg] = min(abs(datacol2-y_neg(k)));
            y_neg(k) = datacol2(ind_neg); % final value
            x_neg(k) = datacol1(ind_neg); % final value

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
        
   
    
    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,'db',minx,maxy,'dr')
plot(minx,miny,'b',minx,maxy,'r')

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');

[Vishnuvardhan Naidu Tanga]

Hello @Mathieu NOE,

Thank you for the revised code. But I think it is considering the Xvalues from the data. But i need to consider the Y values from the data but not from the axis. Can you please help me in modifying it.

[Mathieu NOE]

hello

ok

this is the correction - inner points are defined as 50 % of Y data height -

clc
clearvars
close all

Z = readtable('Atq100.xlsx') ;
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 %%%%%%%%%%%%%%%%%%%%%
            x_init = (maxx(k)+minx(k))/2; % initial guess
            % find nearest value
            aa = round(length(datacol1)/2);
            
            datacol1_pos = datacol1(aa+1:end);
            datacol1_neg = datacol1(1:aa);
            datacol2_pos = datacol2(aa+1:end);
            datacol2_neg = datacol2(1:aa);
            [~,ind_pos] = min(abs(datacol1_pos-x_init));
            [~,ind_neg] = min(abs(datacol1_neg-x_init));
            y_pos(k) = datacol2_pos(ind_pos); % final value
            x_pos(k) = datacol1_pos(ind_pos); % final value
            y_neg(k) = datacol2_neg(ind_neg); % final value
            x_neg(k) = datacol1_neg(ind_neg); % final value
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
    
    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,'db',minx,maxy,'dr')
plot(minx,miny,'b',minx,maxy,'r')

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');

[Vishnuvardhan Naidu Tanga]

Hello @Mathieu NOE,

Thank you so much for the help. It is exactly what i need. Have a nice weekend.

[Mathieu NOE]

My pleasure

Have a nice weekend.too !