Loop output not saving to a cell array. Only last solution saving to cell

clear all
close all
clc

%load data
load('H.mat')
load('facies.mat')
load('q.mat')

%domain size
Nx = 230;
Ny = 240;
Nz = 95;
dx = 100;
dy = 200;
dz = 5;
Lx = Nx*dx;
Ly = Ny*dy;
Lz = Nz*dz;



% particle starting location
x_start = 118*dx+50;  % x starting position of the particle (0,0 is the bottom left corner of the domain)
y_start = 153*dy+100; % y starting position of the particle
z_start = 58*dz;

%Making Particle Tracking Automatic by keeping x&y constant but changing z
for ii=0:50:100
   x_start=118*dx+ii;

%flow    
qx=q.qx;
qy=q.qy;
qz=q.qz;
geometry = facies;

% set porosity value
por = 0.3;

% evaluate velocity from fluxes
vx=-qx./por;              % sign - is for being consistent with sdr 
vy=+qy./por;              % sign + is for being consistent with sdr 
vz=-qz./por;

% evaluate inlet and outlet velocity for each cell

Vxin = vx(:,1:(end-1),:);
Vxout = vx(:,2:end,:);

Vyin = vy(1:(end-1),:,:);
Vyout = vy(2:end,:,:);

Vzin = vz(:,:,1:(end-1),:);
Vzout = vz(:,:,2:end,:);

% seed = 16843592;
% RandStream.setGlobalStream(RandStream('mt19937ar','seed',seed));
% tic

N = 1;
dt=0.05;                                %in days
% % D = 6.093e-11;  			        % diffusion coefficient
D=0;                                    % diffusion/dispersion coefficient
tic
for i=1:N

    [xnew,ynew,znew]=PTrack_function_3D(Nx,Ny,Nz,dx,dy,dz,Lx,Ly,Lz,Vxin,Vxout,Vyin,Vyout,Vzin,Vzout,x_start(i),y_start(i),z_start(i),D,dt,geometry);
end
toc


%%plot trajectory

figure
xv=(0+dx/2:dx:Lx-dx/2);
yv=flip(0+dy/2:dy:Ly-dy/2);
imagesc(xv,yv,geometry(:,:,56))

hold on

plot(xnew,ynew,'.r')
figure
scatter3(xnew,ynew,znew, 'filled', 'r')


end 

I want to save all outputs from the functions. But it only saves the last step of iteration. How can I solve this?

Answer 1

[Raj]

1) Your comment says:

"%Making Particle Tracking Automatic by keeping x&y constant but changing z"

However you are changing x_start inside loop and keeping y and z constant.

2) What is the need for 'for' loop here? (since N is equal to 1 this loop will run only once)

for i=1:N
[xnew,ynew,znew]=PTrack_function_3D(Nx,Ny,Nz,dx,dy,dz,Lx,Ly,Lz,Vxin,Vxout,Vyin,Vyout,Vzin,Vzout,x_start(i),y_start(i),z_start(i),D,dt,geometry);
end

3) Now I understand you are asking about storing xnew,ynew and znew for each iteration of 'for ii=1:50:100'. In that case, you can predefine your outputs as empty arrays and extract the function output to dummy variables. Something like this before your 'ii' loop starts:

xnew=zeros(3,1);
ynew=xnew;
znew=ynew;

Then something like this inside the 'for' loop:

[A,B,C]=PTrack_function_3D(Nx,Ny,Nz,dx,dy,dz,Lx,Ly,Lz,Vxin,Vxout,Vyin,Vyout,Vzin,Vzout,x_start,y_start,z_start,D,dt,geometry);
xnew(ii/50+1,1)=A;
ynew(ii/50+1,1)=B;
znew(ii/50+1,1)=C;

Now at the end of "for ii=1:50:100" loop your xnew,ynew and znew will have 3 elements each corresponding to ii=0 case, ii=50 case and ii=100 case.

4) Shift the plot trajectory portion of code outside the 'for' loop.