Error while solving nonlinear differential equations using ode45

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BISMARK
BISMARK 2021-5-4
评论： BISMARK 2021-5-4
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);
  2 个评论
Alan Stevens
Alan Stevens 2021-5-4
编辑：Alan Stevens 2021-5-4
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
BISMARK 2021-5-4
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

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采纳的回答

Alan Stevens
Alan Stevens 2021-5-4
Then this line
[t,y0]=ode45(@evapmodel,tspan,y0);
should presumably be
[t,y0]=ode45(@evapfunc,tspan,y0);
  3 个评论
显示 1更早的评论
Alan Stevens
Alan Stevens 2021-5-4
Ran in:
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

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