How do you plot markers to specific points?

I have the plot markers added, but they aren't where I need them. They need to be on each line at x= 1,5,9, and 15. How do I achieve this?

[VBBV]

Oneway you can plot markers at specfic points (without using find function) is by creating vector separately and evaluating the equations at those points. Later plot them using hold on

clearvars
x = linspace(1,15,100);
y1 = log(x.^2+4)./(sqrt(2.*x.^2+1));
y2 = sin(x)./log(x.^2)

y2 = 1×100

Inf 3.4370 1.9248 1.3987 1.1153 0.9263 0.7827 0.6638 0.5596 0.4651 0.3772 0.2947 0.2168 0.1431 0.0738 0.0090 -0.0511 -0.1059 -0.1552 -0.1988 -0.2361 -0.2672 -0.2917 -0.3095 -0.3208 -0.3255 -0.3239 -0.3162 -0.3027 -0.2840

% Marker plot
xM = [1 5 9 15];
y3 = log(xM.^2+4)./sqrt(2.*xM.^2+1);
y4 = sin(xM)./log(xM.^2)

y4 = 1×4

Inf -0.2979 0.0938 0.1201

figure
hold on
plot(x,y1,x,y2,'--')
plot(xM,y3,'b+',xM,y4,'r+','MarkerSize',12); grid

[DJ Mckenna]

Thanks a lot!

Answer 1

[Torsten]

The points in the graph you address are x(1), x(5), x(9) and x(15), not x=1, x=5, x=9 and x=15.

Use "find" before plotting to get the respective indices or calculate them by hand.

[Dyuman Joshi]

OP will not obtain the exact values with the current data, as the values 5 and 9 don't exist in x.

The best idea would be use the colon operator to define x -

x = linspace(1,15,100);
min(abs(x-9))

ans = 0.0606

min(abs(x-5))

ans = 0.0404

%create x via colon operator
x0 = 1:0.01:15; %Ideally x0 = (100:1:1500)/100;
min(abs(x0-9))

ans = 0

min(abs(x0-5))

ans = 0

Answer 2

[Walter Roberson]

You have the potential problem that you might not have x coordinates that are exactly 5 or 9 (but exactly 1 and exactly 15 should exist because of the way you linspace()). So if you want markers at x = 5 and x = 9, you have to interpolate positions. The alternative would be to locate the locations in x that are closest to the desired values.

marker_x = [1, 5, 9, 15];
marker_y1 = interp1(x, y1, marker_x);
marker_y2 = interp1(x, y2, marker_x);
h = plot(x, y1, '-', x, y2, '--');
hold on
plot(marker_x, marker_y1, '+', 'Color', h(1).Color);
plot(marker_x, marker_y2, '+', 'Color', h(2).Color);
hold off