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Homework Help: Matlab, how to know time step size in the plot or how can i get the ou

  1. Jul 15, 2014 #1


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    Since i am using matlab ode23s solver, it contains two matlab files . One contain the differential equations and another contains plotting and to run the m-files.
    The code are working perfectly. Now i want to know the time step size that is using on the plot. How can i get the output of time step size. I would like to know the time step size that is using on the plot too. please help me.


    % 3 Nonlinear differential equations after Asymptotic expansion
    % with 1-c in dc/dt differential equation

    Code (Text):
     function xpr= no(t,x)
          %values of parameters
            k_f= 6.7*10.^7;
            k_d= 6.03*10.^8;
            %Unknown parameters
            lambda_b= 0.0087;
            % scale parameters
            K_F= k_f * 10.^-9;
            K_D= k_d * 10.^-9;
            K_N= k_n * 10.^-9;
            K_P= k_p * 10.^-9;
            LAMBDA_B= lambda_b*10.^-9;
            %Pool Values
            P_C= 3 * 10.^(11);
            P_Q= 2.87 * 10.^(10);
         % initial conditions
          %Non-linear differential equations.
          % dc_0/dtau=  c_0*(- K_F - K_D - K_N * s_0 - K_P*(1-q_0))
          % ds_0/dtau = Lambda_B * c* P_C *(1-s_0)
          % dq_0/dtau = (1-q_0)* K_P * c_0 *(P_C / P_Q)
        xpr= zeros(3,1);
        xpr(1)= c_0*(- K_F - K_D - K_N * s_0 - K_P*(1-q_0));
        xpr(2)= LAMBDA_B * c_0* P_C *(1-s_0);
        xpr(3)= (1-q_0)* K_P * c_0 *(P_C / P_Q);
        xpr= [xpr(1);xpr(2);xpr(3)];
    % TO RUN the 3 nonlinear differential equations after asymptotic expansion.
    % with 1-c in dc/dt differential equation

    Code (Text):

         format bank
          close all;
          clear all;
          %time interval
          tspan=[ti tf];
          x0=[0.25 0.02 0.98]; %initial conditions
          %time interval of [0 2] with initial condition vector [0.25 0.02 0.98] at time 0.
          options= odeset('RelTol',1e-4, 'AbsTol',[1e-4 1e-4 1e-4]);
          [t,x]= ode23s(@no,tspan,x0,options);
          %Plotting the graphs:
          subplot(3,1,1), plot(t,x(:,1),'r'),grid on;
          title('3 nonlinear differential equations (with 1-c)'),ylabel('c_0');
          subplot(3,1,2), plot(t,x(:,2),'b'),grid on;
          subplot(3,1,3), plot(t,x(:,3),'g'),grid on;
  2. jcsd
  3. Mar 27, 2017 #2
    I believe your time step sizes should be stored in the 't' vector output from ode23
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