Error while solving nonlinear differential equations using ode45

clear

%parameters are defined

global F1 F2 T1 X1 M C P100 F200 T200 F3

F2=2.0;P100=194.7;F200=208.0;F1=10.0,T1=40.0;X1=5.0;F3=50.0;T200=25.0; M=20.0;C=4.0;

tspan=[0 600] %simulation time

y0=[1.0 25.0 50.5] %arbitrary initial conditions

t=tspan

[t,y0]=ode45(@evapmodel,tspan,y0);

%figures

figure(1),clf

plot(t,y(:,1),t,y(:,2),t,y(:,3),'--')

legend('L2','X2','P2')

xlabel('t')

ylabel('Output Parameters')

Here is the ERROR :(

Unrecognized function or variable 'evapmodel'.

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

[Alan Stevens]

What does your evapmodel function look like, and have you saved it in a separate file, or at the end of the file you've shown? Are you running it from the workspace or the file?

[BISMARK]

The evapmodel is the above code and the evapfunc looks like this. I have saved it in the same file and run it on a separate live editor.

function dydt = evapfunc(t,y)

%evapfunc summary of this function goes here

global F1 F2 T1 X1 M C P100 F200 T200 F3

%calculate other variables

T2 = 0.5616*y(3)+0.3126*y(2)+48.43;

T3 = 0.507*y(3)+55.0;

T100=0.1538*P100+90.0;

Q100=0.16*(F1+F3)*(T100-T2);

F4= Q100-F1*0.07*38.5*(T2-T1)/38.5;

F100=Q100/36.6;

Q200=6.84*(T3-T200)/1+(6.84/0.07*F200);

T201=T200+Q200/F200*0.07;

F5=Q200/38.5;

%Calculation of outputs

dL2dt= F1-F2-F4/20;

dX2dt=F1*X1-F2*y(2)/M;

dP2dt=F4-F5/C;

dydt=[dL2dt;dX2dt;dP2dt];

end

Answer 1

[Alan Stevens]

Then this line

[t,y0]=ode45(@evapmodel,tspan,y0); 

should presumably be

[t,y0]=ode45(@evapfunc,tspan,y0); 

[BISMARK]

I am still getting this same error. I am not sure what i am doing wrong.

Unrecognized function or variable 'evapfunc'.

Error in odearguments (line 90)

f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

[Alan Stevens]

The following works:

global F1 F2 T1 X1 M C P100 F200 T200 F3
F2=2.0;P100=194.7;F200=208.0;F1=10.0;T1=40.0;X1=5.0;F3=50.0;T200=25.0; M=20.0;C=4.0;
tspan=[0 600];  %simulation time
y0=[1.0 25.0 50.5]; %arbitrary initial conditions
t=tspan;
[t,y]=ode45(@evapfunc,tspan,y0); 
%figures
figure(1),clf
plot(t,y(:,1),t,y(:,2),t,y(:,3),'--')
legend('L2','X2','P2')
xlabel('t')
ylabel('Output Parameters')

function dydt = evapfunc(~,y)
 %evapfunc summary of this function goes here
global F1 F2 T1 X1 M C P100 F200 T200 F3
%calculate other variables
T2 = 0.5616*y(3)+0.3126*y(2)+48.43;
T3 = 0.507*y(3)+55.0;
T100=0.1538*P100+90.0;
Q100=0.16*(F1+F3)*(T100-T2);
F4= Q100-F1*0.07*38.5*(T2-T1)/38.5;
F100=Q100/36.6;
Q200=6.84*(T3-T200)/1+(6.84/0.07*F200);
T201=T200+Q200/F200*0.07;
F5=Q200/38.5;
%Calculation of outputs
dL2dt= F1-F2-F4/20;
dX2dt=F1*X1-F2*y(2)/M;
dP2dt=F4-F5/C;
dydt=[dL2dt;dX2dt;dP2dt];
 end

[BISMARK]

Thanks so much. This worked.