Why isn't my graph plotting correctly?

Hi, I think I must be being dense, I am attempting to plot in Matlab, but I am getting a plot that is very wrong.

km=linspace(0,10,100);
y=tan(km)+tanh(km);
plot(km,y,'color','red','LineWidth',1.5);
xlabel('$k_m$','Interpreter','latex');
ylabel('$f(x)$','Interpreter','latex');
title('Graph of $f(x)=tan(k_m)+tanh(k_m)$','Interpreter','latex')

Please could someone explain what I have done wrong to obtain this:

Cheers

[Adam]

What is the graph you are expecting?

[Monkeyman]

[Adam]

I suspect the difference is simply that it is joining asymptotes together in the plot. If you explicitly insert NaNs in your data at the points of the asymptotes (or basically between the points either side of one) this should get rid of that, I think.

Answer 1

[Star Strider]

Set the peaks values to NaN and they will not plot:

km=linspace(0,10,1000);
y=tan(km)+tanh(km);
[pks,locs] = findpeaks(y);                                          % Locate Peaks Peaks
y(locs) = NaN;                                                      % Set Peaks To ‘NaN’
plot(km,y,'color','red','LineWidth',1.5);
xlabel('$k_m$','Interpreter','latex');
ylabel('$f(x)$','Interpreter','latex');
title('Graph of $f(x)=tan(k_m)+tanh(k_m)$','Interpreter','latex')
ylim([-6 +6])
grid

[Monkeyman]

That's great, thank you. Is there a variation of the findpeaks that works for a function handle like below? I can't find one. I am trying to find the roots closest to certain values using x=fzero(f,km) but they are not compatible. Any help would be really appreciated!

f=@(km) tan(km)+tanh(km)

[Star Strider]

To the best of my knowledge, findpeaks will not work on function handles. If you want to use fzero to find the zero-crossings, this is an appropriate approach:

km = linspace(0,10,100);
y = tan(km)+tanh(km);
[pks,locs] = findpeaks(y);                                          % Locate Peaks Peaks
y(locs) = NaN;                                                      % Set Peaks To ‘NaN’

f=@(km) tan(km)+tanh(km);
midpt = fix(mean(diff(locs))/2);
for k = 1:numel(locs)
    idx = min([numel(km) locs(k)+midpt]);                           % Prevents Indexing Beyond ‘km’ Length
    zro(k) = fzero(f, km(idx));
end

It returns the zero-crossings in the ‘zro’ vector.

Experiment to get the result you want.