if statements inside of while loop

I would like to run this while loop for a inputted number of cycles. but if the input's at any point through out those cycles cause one of my equations to output to be <= 0 then I would like that equation to just output 0 for then on. I think that can be done with an if statement between each of my top 3 eaquations but I'm not sure how to do it. any help would be appreciated.

% Predator-Prey Model Equations
clear,clc
% variables, we have to set these at the begin
d0=input('Enter Starting population of Deer: ');
m0=input('Enter Starting population of Moose: '); 
w0=input('Enter Starting population of Wolves: '); 
y=input('Enter Number of years to graph: ');
i=1;
k=1;
%fixed rates
a=.0035; % Deer repop rate
b = .0004; % Rate wolves find deer
c=.0029; % Moose repop rate
e=.00039; % rate wolves find moose
f=.15; % wolves effiecency at making food into offspring (repop rate)
g = .07;  % Death rate of wolves
%h=.05; % an added death rate that could be used if you wanted to add in
%deaths from people or other animals
%equations
% D=d0+d0^2*A-B*d0^2*w0-d0^2*H;
% M=m0+m0^2*C-E*m0^2*w0-m0^2*H;
% W=w0+w0^2*F-w0^2*G;

%plot %
% here is the general idea for the plot these equations don't have the
%extra death rate like we talked about, those can be added
while k<=y
    d(i)=d0+((d0^2)/2)*a-((d0^2)/2)*b*w0; % a=Deer repop rate  b=rate wolves find deer
    m(i)=m0+((m0^2)/2)*c-((m0^2)/2)*e*w0;% c= Moose repop rate  e= rate wolves find moose
    w(i)=w0+((w0^2)/2)*f*(m0*b+d0*e)-g*w0; %f= wolves effiecency at making food into offspring  g= death rate of wolves
    d0=d(i);
    m0=m(i);
    w0=w(i);
    i=i+1;
    k=k+1;
end
%plotting
plot(1:i-1, d, 'o');
title('Deer Over Time')
grid on
axis([0, i, 0, 100000])
plot(1:i-1, m, 'o')
grid on
axis([0, i, 0, 100000])
title('Moose over time')
plot(1:i-1, w, 'o')
grid on
axis([0, i, 0, 25])
title('wolves over time')
%display final outputs
disp('Final amount of deer')
disp(d0)
disp('Final amount of Moose')
disp(m0)
disp('Final amount of Wolves')
disp(w0)

Answer 1

[Ameer Hamza]

You can just break the loop at that point.

flags = false(1,3);
while k<=y
    if flags(1)
        d(i) = 0;
    else
        d(i)=d0+((d0^2)/2)*a-((d0^2)/2)*b*w0; % a=Deer repop rate  b=rate wolves find deer
        if d(i) < 0
            flags(1) = true;
        end
    end
    
    if flags(2)
        m(i) = 0;
    else
        m(i)=m0+((m0^2)/2)*c-((m0^2)/2)*e*w0;% c= Moose repop rate  e= rate wolves find moose
        if m(i) < 0
            flags(2) = true;
        end
    end
    
    if flags(3)
        w(i) = 0;
    else
        w(i)=w0+((w0^2)/2)*f*(m0*b+d0*e)-g*w0; %f= wolves effiecency at making food into offspring  g= death rate of wolves
        if w(i) < 0
            flags(3) = true;
        end
    end
    
    d0=d(i);
    m0=m(i);
    w0=w(i);
    i=i+1;
    k=k+1;
end

[Tanner Smith]

thanks, but I would like the while loop to continue so you can see what happens to the other equations when one of them hits zero or less. I just don't want the equation that hit a negative number to suddenly grow again. so if d goes negative i want d to stay at zero and the other equations to continue. Is this possible

[Ameer Hamza]

Ok. There was a bit of misunderstanding. Try the updated answer.

[Tanner Smith]

thanks again for the help, this might be closer to what I am looking for. but when I try and run this code it says "Index exceeds the number of array elements (1)." or something of that sort when i input numbers that would have given me trouble. it doesn't mind numbers that were already working.

[Ameer Hamza]

There was an error in the code. I have updated the code. Try it now. Also, if there is some other message, I suggest to paste the complete error message (Everything in red text)

[Tanner Smith]

thanks for the help

[Ameer Hamza]

I am glad to be of help.