matlab求解微分方程报错

软件情况：64位matlab-R2019a需要用到：Symbolic Math Toolbox

这是程序代码

[function Fin = f(t)

f0=0.012;

t1=5;

tend=360;

a=0.5;

if t>=t1 && t<=tend

Fin = (1+a)*f0;

elseif t>0 && t<t1

Fin = f0+(a*f0)/t1.*t;

elseif t>tend && t<tend+t1

Fin = (1+a)*f0-(a*f0)/t1.*(t-tend);

else

Fin=0.012;

end

end

t=0:1:800;

n=length(t);

fin=[];

for i=1:n

Fin=f(t(i));

fin=[fin Fin];

end

Vv=[];

for i=1:n

Vv1=dsolve('Dvv=fin(i)-0.012*(vv/0.0237)^2/(35*0.012*(vv/0.0237)^-0.5-1)','0.23') ;

Vv=[Vv Vv1];

end]

报错的位置主要在Vv1=dsolve('Dvv=fin(i)-0.012*(vv/0.0237)^2/(35*0.012*(vv/0.0237)^-0.5-1)','0.23') ;这一句，当我去掉后面的参数'0.23时'，可以运行，但求不出解析解，执行结果如下

警告: Unable to find explicit solution. Returning implicit solution instead.

> In dsolve (line 208)

In Untitled (line 10)

当我加上'0.23'这个参数时，反而报错不能运行了，运行结果如下

错误使用 mupadengine/feval (line 195)

Invalid equations.

出错 dsolve>mupadDsolve (line 340)

T = feval(symengine,'symobj::dsolve',sys,x,options);

出错 dsolve (line 194)

sol = mupadDsolve(args, options);

出错 Untitled (line 10)

Vv1=dsolve('Dvv==(fin(i)-0.012*(vv/0.0237)^2/(35*0.012*(vv/0.0237)^-0.5-1))','0.23') ;

Answer 1

[Anjaneyulu Bairi]

Hi,

I understand that you are getting error while solving differential equation using “dsolve” function. The “dsolve” function should have second argument as condition like vv(0)=0.23. Change the second argument to 'vv(0)=0.23' and it works.

Visit the following documentation link for more information on “dsolve” - https://in.mathworks.com/help/symbolic/dsolve.html

Hope it helps to resolve your query.