Finding instantaneous BPM in EKG signal with a threshold

Hello,

I have this assignment where I have to find the instantaneous BPM of an EKG signal.

I did the first exercise where it was required to find a threshold.

Now my idea to calculate the BPM is to find the amount of times the threshold cuts the EKG signal and divide by 2(because it cuts each peak 2 times):

But when I run the code it does not seem to be reading the code in the if statement. I assume this might be the case because thefunction is not contnuous at every point but just connects discrete values?

Please help.

Code:

[t, data] = load_data("UE1.txt", 100);
N= 1:length(data);
average = mean(data);
threshold = max(data)*0.15;
vec = ones(1,length(data));
vec = vec.*threshold;
figure();
data = data';
vec = vec';
hold on
plot(t,data,'r');
plot(t, vec,'r--');
j=0;
for i = N
    if data(i) == vec(i)
        j = j+1;
        disp(j);
    end
end