Why do I get repeated values for a variable when its parameters change with every iteration?

I have a code, and I was figuring out the equations to plug into my for loops, testing as I went. The initial run throughs were fine, yielding results that weren't quite correct, but were expected. Now, while I think I have my final equations, the variable that I would like to see is getting repeating values, and I do not know why.

In my code V3 should equal A2 times V2 times 1.1, all divided by A3. A3 is constant, but A2 and V2 change with every loop iteration. However V3 is getting repeating resutls.

Code Below

Thank You

clc;
clear all;
close all;


%Define variables
d1 = .05; %m
A1 = (pi/4)*d1^2;%m^2
d3 = .01; %m
A3 = (pi/4)*d3^2;%m^2
d2 = (0.1:.1:0.5).*d1;%m
A2 = (pi/4)*d2.^2;%m^2
L = 0.5; %m
h = 3; %m
rho = 1000; %kg/m^3
Pt = [500 750 1000].*1000; %Pa gauge
g = 9.81; %m/s^2

%Preallocation Matrices
Vave = zeros();%m/s
Ptube = zeros();%Pa
V3 = zeros();%m/s
V1 = zeros();%m/s
V2 = zeros();%m/s

%Loop to iterativly calculate Vave, Ptube, V2, and V3
for j = 1: length(Pt)
     for k = 1:length(d2)
    
        Vave(j,k) = sqrt((Pt(j)*A1 +rho*g*h*A1)/((((rho*A1)/2)+...
            ((0.002*rho)/2)*(2*pi*(d1/2)*L)+2*pi*(d1/2)^2)));
        
        Ptube(j,k) = Pt(j) + rho*g*h-(rho*0.002*Vave(j,k).^2)/2;

        V2(j,k) = (A1*Vave(j,k))./(A2(k)*(.1+1));
        
        
        V3(j,k) = (A2(k).*V2(j,k)*(1.1))/A3;
      end
end



plot(V3, d2);
xlabel('Nozzle Velocity (m/s)');
ylabel('Pump Jet Nozzle diameter (m)');
legend('Pt = 500kPa', 'Pt = 750kPa', 'Pt = 1000kPa', 'location', 'southeast');

Answer 1

[David Goodmanson]

Hi Michael,

Vave(j,k) and Ptube(j,k) are assigned values that depend on row index j but not column index k, so each row contains all identical values. V2(j,k) brings in k dependence by dividing by A2(k), so those matrix elements change with the column index k. But V3(j,k) comes back and multiplies v2(j,k) by A2(k), canceling out the previous k dependence and leaving rows with identical values again.

[Michael Jolibois]

Thank you for clarifying, David. Is there a way keep these relations but prevent that from happening?

I have tried changing V3 to equal Vave(j,k) times A1 divided by A3, but the same thing happens as Vave is the same number for each iteration of k.

[David Goodmanson]

Hi Michael, the same equations have the same solutions, so if you suspect something is wrong you will have to check the underlying equations.

[Michael Jolibois]

That's the conclusion I reached too. Thank you for your help.