Why isn't my graph plotting correctly?
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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.
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
3 个评论
Adam
2019-11-12
What is the graph you are expecting?
Monkeyman
2019-11-12
Adam
2019-11-12
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.
回答（1 个）
Star Strider
2019-11-12
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
2 个评论
Monkeyman
2019-11-12
Star Strider
2019-11-12
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.
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2019-11-12
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