How to plot a maximum value on an existing line graph

I am currently using assigned data to plot two three matrices as line graphs in a sublot, they are both 25x1 matrices.

X=Cell mass concentration

t= time (hours)

Ethanol= ethanol concentration

I also need to plot max(X) as a single point on this plot, but every time i try, it appears as a separate line (with a slope of 0) on the graph instead of marking the point.

here is my code and graph:

A=figure

x=[t];

y1=[Ethanol];

y2=[X]

subplot(1,2,1); plot(x,y1);

hold on

plot(x, max(Ethanol), 'r*');

%Labeling

title('Time vs. Cell Mass Concentration');

xlabel('Time (hours)');

ylabel('Ethanol (g/L)');

subplot(1,2,2); plot(x,y2);

%Labeling

title('Time vs. Ethanol');

xlabel('Time (hours)');

ylabel('Cell Mass Concentration (g/L)');

in the image you can see what happens as a currently try and plot the max value (subplot plot 1) and what the graph looks like without even attempting to plot the max value (subplot plot 2)

Answer 1

[Ruger28]

Please use the code formatting.

A=figure
x=[t];
y1=[Ethanol];
y2=[X]
% Plot frst graph
subplot(1,2,1); 
plot(x,y1);
hold on
% find max of Ethanol
[maxVal,maxIDX] = max(Ethanol);
% for single point plotting, use scatter
scatter(x(maxIDX), maxVal, 'r*'); % plot max of Ethanol with its corresponding x value
%Labeling
title('Time vs. Cell Mass Concentration');
xlabel('Time (hours)');
ylabel('Ethanol (g/L)');
subplot(1,2,2); plot(x,y2);
%Labeling
title('Time vs. Ethanol');
xlabel('Time (hours)');
ylabel('Cell Mass Concentration (g/L)');

[Grace Rembold]

Thank you so much, this worked wonderfully!

[Wakeel Mohammed]

Thank you sooo much

Answer 2

[David Goodmanson]

Hi Grace,

Here is an example of what I think you are looking for. The idea is to use the second output of max to find the index in the x vector where the max occurs, and plot just that one point.

x = 0:.001:5;
y = 1+2.3*x-x.^2+.11*x.^3;
[maxy ind] = max(y)
plot(x,y,x(ind),y(ind),'o')
% or
% plot(x,y,x(ind),maxy,'o')
grid on