Error in Ode 45

I have a probleb solving this ode ODE it gives me the following errors

or too many inputs in the ode45

or Inputs must be floats, namely single or double.

burn_time=100;
Nt=1000;
m_ox=0.7;
t=linspace(0,burn_time,Nt);
m_ox=m_ox.*ones(1,Nt);
Dp_in=0.0005;
rho_fuel=1.9;
L_grain=0.5;
%% Definizione regression rate
a=0.007;
b=0.67;
r_dot=a.*m_ox.^b;% in futuro r_dot sara gia fornito da dati sperimentali


C=((m_dot_fuel+m_ox-m_dot_pr)./(v_cham)) ;


A=((4.*r_dot)./Dp_t);
dt=t(2)-t(1);
t_span=(0:dt:burn_time);
y_0=zeros(1,Nt);
y_0=y_0(:);
[T,Y ]=ode45(@(t,y) vdp1(C,y,A),t_span,y_0);
function dydt = vdp1(C,y,A)


dydt =C+A*y;
dydt=dydt(:);
end

Answer 1

[Star Strider]

The problem here:

[T,Y ]=ode45(@(t,y) vdp1(C,y,A),t_span,y_0);

is that one of the input arguments to ‘vdp1’ needs to be ‘t’.

There are too many missing constants for me to run your code, however this:

[T,Y ]=ode45(@(t,y) vdp1(t,C,y,A),t_span,y_0); 

should work, if there are no other problems.

[Francesco Renzulli]

clc;
close all;
clear all;
%% Parametrizzazione DEL FLUSSO DI OSSIDANTE 
%In futuro questa parte di codice verrà sostiutita dal grafico excel, che
%ci indichera si ala discretizzazione temporale che i valori della funzione
%m_ox
burn_time=100;
Nt=1000;
m_ox=0.7;
t=linspace(0,burn_time,Nt);
m_ox=m_ox.*ones(1,Nt);
Dp_in=0.0005;
rho_fuel=1.9;
L_grain=0.5;
%% Definizione regression rate
a=0.007;
b=0.67;
r_dot=a.*m_ox.^b;% in futuro r_dot sara gia fornito da dati sperimentali
%% variabili ugello divergente 
At =1.45*10^(-4);%Area della gola del' ugello 
P_e=1*10^6;% Pressione in uscita 
P_cham=45*10^6;
gamma=1.2;
T_cham=3000;
R=0.344;

 %% Ugello isoentropico
 T_e=T_cham*(P_e/P_cham)^((gamma-1)/gamma);
 sound_v=(gamma*R*T_e)^0.5;
 T_t=(2*R*gamma*T_cham)/(gamma-1);

 v_e=(T_t*(1-((P_e/P_cham)^((gamma-1)/gamma))))^0.5;
 M_e=v_e/sound_v;
 
 %Pt=P_e*(1+((gamma-1)/2)*M_e^2)^((gamma)/(gamma-1));
 Pt=P_cham*(T_cham./T_t)^(gamma/(gamma-1));
 %Pt=((2/(gamma+1))^(gamma/(gamma-1)))*2.068;
 
 

 m_dot_pr=(At*Pt)/(((T_t)^0.5))*((gamma/R)^0.5)*((gamma+1)/2);



%% Calcolo il variare del DIameter port
syms Dp(T) T

ode=diff(Dp,T)==2.*r_dot;
cond=Dp(0)==Dp_in;
Dp=dsolve(ode,cond);
Dp_t=subs(Dp,T,t);

%% Calcolo la variazione di volume della C.C e dell' afflusso di carburante nel tempo 

m_dot_fuel=r_dot.*rho_fuel*L_grain.*Dp_t;
v_cham=((Dp_t./2).^2).*L_grain;
plot(t,m_dot_fuel);
figure(2)
plot(t,v_cham);
%% Calcolo la variazione di densita risolvendo il sistema lineare 



C=((m_dot_fuel+m_ox-m_dot_pr)./(v_cham)) ;


A=((4.*r_dot)./Dp_t);
dt=t(2)-t(1);
t_span=(0:dt:burn_time);
y_0=zeros(1,Nt);
y_0=y_0(:);

[Francesco Renzulli]

Thank yo a lot for the answer

this is all the code that there is before and I tried like you have said but it gives the error

Inputs must be floats, namely single or double.

[Francesco Renzulli]

This is the part where I have problem, and is the continuation of the code from y=y(:)

[T,Y ]=ode45(@(t,y) vdp1(t,C,y,A),t_span,y_0);
function dydt = vdp1(t,C,y,A)


dydt =C+A*y;
dydt=dydt(:);
end

even putting t in vdp1 it gives error

kind regards

[Star Strider]

One change:

%% Calcolo il variare del DIameter port
syms Dp(T) T

ode=diff(Dp,T)==2.*r_dot;
cond=Dp(0)==Dp_in;
Dp=dsolve(ode,cond);
Dp_t=subs(Dp,T,t);
Dp_t = double(Dp_t);                                % <— ADD THIS LINE TO CONVERT THE SYMBOLIC VECTOR TO A DOUBLE VECTOR

is necessary, then your code runs without error. The added assignment converts the symbolic vector to a double vector.

[Francesco Renzulli]

thanks a lot you solved it, it runs ....

[Star Strider]

As always, my pleasure!