The last entry in tspan must be different from the first entry. Error in ode45 (line 115) odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

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Anne Louise Barão 2020-7-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/569319-the-last-entry-in-tspan-must-be-different-from-the-first-entry-error-in-ode45-line-115-odear

评论： Anne Louise Barão 2020-7-23

I found this code in an article and tried to run it on my 2014 matlab, but it is giving error on ODE45. The functions are in different programs, but in the same folder. I can't run it. Can someone help me?

function Q=q(t)
global Qstar
DQ=1;
Q=Qstar+DQ;
end
function Hdot=hdot(t,H)
global RHO G A1 A2 Hstar Qstar
Q=q(t);
k1=-A2*sqrt(2*G)/A1;
k2=1/RHO/A1;
Hdot=k1*sqrt(H)+k2*Q;
end
%Physical constants
global RHO G A1 A2 Hstar Qstar
RHO=1000; %(kg/m3)
G=9.8; %(m/sec2)
A1=pi/4; 
A2=pi/400; %(m2)
Hstar=1; %(m)
Qstar=34.7711; %(kg/sec)
% Nonlinear step response
t0=0; %Initial time (sec)
tf=300; %Final time (sec)
H0=Hstar; %Steady-state value (m)
[tn,H] = ode45('Hdot',t0, tf, H0);
DHn=H-Hstar; % Subtract Hstar to obtain DH
% Linear step response
t=0:0.1:300;
k2=1/RHO/A1;
Omega=A2^2*G*RHO/A1/Qstar;
num=k2; 
den=[1 Omega];
DH=step(num,den,t);
% Plot results in centimeters (cm)
plot(t,100*DH,tn,100*DHn,'--'); grid
xlabel('Time (sec)'), ylabel('DH (cm)')

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Answer 1

Walter Roberson 2020-7-23

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https://ww2.mathworks.cn/matlabcentral/answers/569319-the-last-entry-in-tspan-must-be-different-from-the-first-entry-error-in-ode45-line-115-odear#answer_469599

在 MATLAB Online 中打开

[tn, H] = ode45 ('Hdot', [t0, tf], H0);

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Walter Roberson 2020-7-23

在 MATLAB Online 中打开

It works for me.

%Physical constants
global RHO G A1 A2 Hstar Qstar
RHO=1000; %(kg/m3)
G=9.8; %(m/sec2)
A1=pi/4; 
A2=pi/400; %(m2)
Hstar=1; %(m)
Qstar=34.7711; %(kg/sec)
% Nonlinear step response
t0=0; %Initial time (sec)
tf=300; %Final time (sec)
H0=Hstar; %Steady-state value (m)
[tn,H] = ode45(@hdot,[t0, tf], H0);
DHn=H-Hstar; % Subtract Hstar to obtain DH
% Linear step response
t=0:0.1:300;
k2=1/RHO/A1;
Omega=A2^2*G*RHO/A1/Qstar;
num=k2; 
den=[1 Omega];
DH=step(num,den,t);
% Plot results in centimeters (cm)
plot(t,100*DH,tn,100*DHn,'--'); grid
xlabel('Time (sec)'), ylabel('DH (cm)')