How can I retrieve variables from a nested function and use them on the parent function?

Hey guys, I have a little problem here with variables on nested functions. Here is the code:

 function Parent
 %code goes here

    function dx = odestribeck (t,x)
    dx=[x(2);-(Fc*tanh(x(2))+sig2*x(2)+(Fs-Fc)*exp(-(x(2)/Vstri)^2)+k*x(1))/m];
    ode = @odestribeck;
    alg;

          function alg
              [t,x]=ode15s(ode,[0,5],[0,5]);
          end

    end

 %Command to plot variables t and x defined on function alg goes here.
 end

As written on the code, I want to include a plot command on the parent function to the variables t and x defined on alg function (second level nested function).

Thank you in advance!

Answer 1

[David Young]

Edit: The answer below addressed the question of how to get results from nested functions, but doesn't adequately take into account the need to provide the correct function handle argument to ode15s. See the comments. Anyone more expert in using the ode solvers: please contribute!

One method is to return t and x from odestribeck in the normal way:

 function Parent
    ...
    [t,x,dx] = odestribeck(...);
    plot(t,x);
    ...
    function [t, x, dx] = odestribeck (t,x)
      ...
      alg;
      function alg
        [t,x]=ode15s(ode,[0,5],[0,5]);
      end  
    end
  end

Note that the call to plot can go after the nested function definition if you like, but it's probably clearer to leave it with the other code in Parent, before the nested definitions - it doesn't affect the order of execution.

Alternatively, you can make t and x global to both the nested functions, by initialising them in Parent and not passing them as arguments:

 function Parent
    ...
    t = ...;
    x = ...;
    dx = odestribeck;
    plot(t,x);
    ...
    function dx = odestribeck
      ...
      alg;
      function alg
        [t,x]=ode15s(ode,[0,5],[0,5]);
      end  
    end
  end

Again, you can put code after the nested function definitions if you wish.

[Lucas Carvalho]

I aprecciate your answer but it didn't work. By declaring t and x first, matlab accpets to do the charts but don't assume the new calculated values for both of them.

 t = zeros(1,80);
 x = zeros(1,80);
 % [t,x,dx]=odestribeck(t,x)

   function [t,x,dx]=odestribeck(t,x)
  dx=[x(2);-(Fc*tanh(x(2))+sig2*x(2)+(Fs-Fc)*exp((x(2)/Vstri)^2)+k*x(1))/m];
  ode = @odestribeck;
  alg;

    function alg
        [t,x]=ode15s(ode,[0,5],[0,5]);
    end

 end
        subplot(3,1,2)
        plot(t,x(:,1))
        grid('on')
        subplot(3,1,3)
        plot(t,x(:,2))
        grid('on')

It plots obviously nothing because both t and x vectors are zeros.

[Lucas Carvalho]

I just tried to take the second level nested function out and put it as a command on the parent function:

 function [t,x,dx]=odestribeck(t,x)
dx=[x(2);-(Fc*tanh(x(2))+sig2*x(2)+(Fs-Fc)*exp(-(x(2)/Vstri)^2)+k*x(1))/m];
ode = @odestribeck;
 end
 [t,x]=ode15s(ode,[0,5],[0,5]);
        subplot(3,1,2)
        plot(t,x(:,1))
        grid('on')
        subplot(3,1,3)
        plot(t,x(:,2))
        grid('on')

The problem is that the function handle ode doesn't recall any value. I hoped that it would take all odestribeck function calculated values with it, but it didn't work as well.

[David Young]

Sorry - I hadn't noticed when I wrote my answer that odestribeck is the function argument to the solver. I was focused on the idea that the core problem was getting information to and from nested functions, but it's not so simple.

I think your second comment is in the right direction - that is, you should simplify the structure - my suggestion would be

function Parent

   ...
  [t,x]=ode15s(odestribeck,[0,5],[0,5]);
  plot(t, ...);

      function dx = odestribeck (t,x)
          dx=[x(2);-(Fc*tanh(x(2))+sig2*x(2)+ ...
                    (Fs-Fc)*exp(-(x(2)/Vstri)^2)+k*x(1))/m];
      end

end

If this is still unsuccessful, I am not sure what the problem is. It may be worth posting another question, but focusing on the ode solver rather than on the nested function structure, to get a more expert reply.