How can I create a matrix to store my data?

I have phi and alpha scales very from 0:0.1:1 ..I want to create matrix(z) store all the data result (t_star1) for plot pcolor

clear all
clc
global phi alpha r1 r2 k1 k2 b1 b2
r1=0.01;
r2=0.01;
k1=1;
k2=0.5;
b1=0.6;
b2=0.1;
format short
ctr=0;
for phi= 0:0.1:1
  for alpha =0:0.1:1
      y0=[0.99, 0.01,0.0];
      t=[0 :10: 4000];
      [t, y]=ode15s(@n_v_w_ode,t,y0);
      X=[y(:,1),y(:,2),y(:,3)];
      [row_t col_y]=size(X);
      t_star1=-1;
      for i=1: row_t -1
        if X(i,1) > X(i,2) & X(i+1,2) > X(i+1,1)
          n1=X(i,1);
          n2=X(i+1,1);
          v1=X(i,2);
          v2=X(i+1,2);
          t1=t(i);
          t2=t(i+1);
          t_star1=((n2-n1)*t1+v1*(t2-t1)-n1*(t2-t1)-(v2-v1)*t1)/(n2-n1-v2+v1);
        end
      end
      ctr=ctr+1
      u(ctr)=phi
      b(ctr)=alpha
      t_star1=t_star1
      z=zeros(length(phi),length(alpha))
      for k=1:length(phi)
          for  s=1: length(alpha)
              z(k,s)=t_star1
          end
      end
  end
end
figure(1)
pcolor(z);
shading flat; colormap jet; colorbar
xlabel('\alpha')
ylabel('\phi')
title('o^o')

[Jan]

I do not understand the question. The code does not get clear to me also, e.g.:

t_star1=t_star1   ?!?

t_star1 is overwritten in each iteration inside the "for i" loop, when the X(i,1) > X(i,2) & X(i+1,2) > X(i+1,1) is true. Is this intended?

Answer 1

[Matt Tearle]

The loops for z aren't going to achieve anything because phi and alpha are scalars, so all you're really doing is z = t_star1;

As far as I can tell what you're doing, it looks like you're solving an ODE each time with different values for phi and alpha, then calculating some (scalar?) value t_star1 from the solution, and I assume you want to see t_star1 as a function of phi and alpha. I also assume that phi and alpha are referenced in your ODE function n_v_w_ode, along with the other parameters that are listed as global. First, get rid of global! Rewrite n_v_w_ode to take as many inputs as needed, starting with t and y. Then:

phi = 0:0.1:1;
alpha = 0:0.1:1;
nphi = length(phi);
nalpha = length(alpha);

y0=[0.99, 0.01,0.0];
tin=[0 :10: 4000];

z = zeros(nphi,nalpha);
for j = 1:nphi
  for k = 1:nalpha
    % make a function handle to the ODE, with parameters embedded
    f = @(t,y) n_v_w_ode(t,y,phi(j),alpha(k),r1,r2,...);
    % solve ODEs
    [t, y]=ode15s(f,tin,y0);
    X = y(:,1:3);
    % etc etc, get t_star1
    z(j,k) = t_star1;
  end
end
pcolor(z)  % etc

All that stuff to get t_star1 could possibly be cleaned up, but I can't figure out the logic of it just by looking at it right now.

None of the stuff from ctr = ctr+1 to the end of the loop looks necessary to me.