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# how can I improve the logic of this code

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summyia qamar on 8 Jan 2018
Closed: MATLAB Answer Bot on 20 Aug 2021
Im trying to build a relation between supply demand and price using 3 equations. the code I've generated is given below
clear all;
clc;
T=100;
P=zeros(1,T);
D=zeros(1,T);
R=zeros(1,T);
P(1)=10; %Initial Price
D(1)=10; %Initial Demend
R(1)=5; % Initial Resource available
K=100; %Maximum demand
M=10; %maximum resource
N=50; %Max Price K/N=2; N/K=0.5; N/M=5; M/K=0.1
for t=2:T
D(t)=D(t-1)+((1-(P(t-1)/N))*(K/N));
P(t)=P(t-1)-((1-(D(t-1)/K))*(N/K))+((1-(R(t-1)/M))*(N/M));
R(t)=R(t-1)+((1-(D(t-1)/K)*(M/K)));
end
Xvals=1:T;
plot(Xvals,D,'b',Xvals,P,'r',Xvals,R,'g')
legend('Demand','Price','Resource')
when I run the code, the values get below zero. I want that whatever the results are but the values remain positive since neither of price nor demand nor resources can be negative. can anybody help me in improving these equations?

Walter Roberson on 8 Jan 2018
You could do things like
D(t) = max(0, D(t-1)+((1-(P(t-1)/N))*(K/N)) );
This will substitute 0 if the value would have been negative.

Image Analyst on 8 Jan 2018
To clip values to 0, use this code after the loop but before you call plot.
% If arrays are below zero, then clip arrays to 0.
D = max(D, 0);
P = max(P, 0);
R = max(R, 0);