How can I repeat a cycle in a for loop with n samples

for n=1:N
  if t>=Tc
      t=0;
  end
  if t<Ti
      Pmus(n)=A*(t/Ti);
      Pm(n)=5;
  else 
      Pmus(n)=A*(exp(-4*(t-Ti)/Te)-exp(-4))/(1-exp(-4));
      Pm(n)=0;
  end 
      t=t+1;
end

I have to simulate the muscular pressure in a lung, which has the function A*(t/Ti) for when t is smaller than the inspiratory time and the other function for when t is larger than the inspiratory time (but smaller than the inspiratory and expiratory time combined). After t has reached Tc(=Ti+Te), I want the cycle to start anew, but how do I do that, when I have a set number of samples (I need those in another function as well)?

[Birdman]

Is this your entire code? If not, can you share your entire code?

[Lotte Vermeulen]

R=0.0037                        %De weerstand in cm H2O/(ml/s)
FRC=2800;                       %De functionele residuale capaciteit in ml
Clt=100;                        %De compliantie van de gehele long in ml/cm H2O
Va(1)=2800;                     %De initiële waarde van het alveolaire volume in ml
Tstart=0;                       %De begintijd in s
Ts=0.01;                        %De sampletijd in s
Tf=20;                          %De eindtijd in s
A=5;                            %De amplitude van de spierdruk in cm H2O
Ti=1.67;                        %De inspiratietijd in s
Te=3.33;                        %De expiratietijd in s
Tc=5;                           %De tijd van een ademhalingscyclus
N=(Tf-Tstart)/(Ts)+1;

for n=1:N
  if t>=Tc
      t=0;
  end 
  if t<Ti
      Pmus(n)=A*(t/Ti);
      Pm(n)=5;
  else 
      Pmus(n)=A*(exp(-4*(t-Ti)/Te)-exp(-4))/(1-exp(-4));
      Pm(n)=0;
  end 
      t=t+1;
end  

for n=1:N    
  fa(n)=(Va(n)-FRC)/(R*Clt)+(Pmus(n)+Pm(n))/R;
  if n<N
      Va(n+1)=Va(n)+Ts*fa(n);
      Va(n)=Va(n+1);
      n=n+1;
  end
end

t=0:Ts:Tf;
subplot(2,1,1);
  plot(t,Va);
subplot(2,1,2);
  plot(t,Pmus);

This is the whole code

[Birdman]

Undefined function or variable 't'.

[Lotte Vermeulen]

Yes, t is the time (defined before the plot), but I don't really know how to implement it here, because I need to work with n as well because of the plots

Answer 1

[Guillaume]

I'm not entirely clear on what you're asking. As it is your code can be simplified to:

%no loop needed
Pmus = [A*((0:Ti-1)/Ti), A*(exp(-4*(0:Tc-Ti-1)/Te) - exp(-4)) / (1-exp(-4))];
Pm = [5*ones(1, Ti), zeros(1, Tc-Ti)];

If you want to repeat that for several cycles:

Pmus = repmat(Pmus, 1, numcycles);
Pm = repmat(Pm, 1, numcycles);

[Lotte Vermeulen]

I need to simulate some respiratory cycles, with regard to the muscle pressure (pmus) the artificial pressure (pm), the alveolar volume (Va) and the alveolar flow (fa). But this doesn't work, as Ti isn't an integer, so the matrix can't be made

[Guillaume]

The way you wrote your original code, it would only have worked if Ti, Tc, and Te were integers much greater than 1, as your time step was 1. So I went with that assumption.

Never mind, it's easily modified for non-integer time steps, smaller than 1. Again, there really is no need for loop. All you do is create a vector of time steps with as many steps as you want:

A=5;
Ti=1.67;                        %De inspiratietijd in s
Te=3.33;                        %De expiratietijd in s
Tc = Ti + Te;                   %safer than hardcoding the value
numsteps = 100;                 %for example

t = linspace(0, Tc, numsteps);

Pmus and Pm can then be calculated in just one line each:

Pmus = [A*t(t<Ti)/Ti, A*(exp(-4*(t(t>=Ti)-Ti)/Te) - exp(-4)) / (1-exp(-4))];
Pm = [5*ones(1, sum(t<Ti)), zeros(1, sum(t>=Ti))];
plot(t, [Pmus; Pm]);

You can of course repeat that for how many cycles you want, using repmat:

numrepeat = 5;
trepeat = reshape(t' + (0:numrepeat-1) * t(end), 1, []);  %requires R2016b or later
Pmusrepeat = repmat(Pmus, 1, numrepeat);
Pmrepeat = repmat(Pm, 1, numrepeat);
plot(trepeat, [Pmusrepeat; Pmrepeat]);

edit: it looks like Ts is your sampling period. In that case, instead of using linpace to build the t vector use the colon operator:

t = 0:Ts:Tc;

The rest is still the same.

Answer 2

[Torsten]

t=Tstart;
n=1;
cycle=1;
flag=0;
while flag==0
  if t<Ti
      Pmus(n,cycle)=A*(t/Ti);
      Pm(n,cycle)=5;
  else 
      Pmus(n,cycle)=A*(exp(-4*(t-Ti)/Te)-exp(-4))/(1-exp(-4));
      Pm(n,cycle)=0;
  end 
  t=t+Ts;
  n=n+1;
  if t>Tf
    cycle=cycle+1;
    n=1;
    t=Tstart;
  end
end