how to plot a fourth ordinary differential equation

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Lorenzo Mereu
Lorenzo Mereu 2021-3-8
回答： David Jacob 2021-3-8
Hi, I'm new on matlab and maybe this could be a silly answer. I solved this fourth order differential equation, but I have some problems with the function "fplot(usol(x))". Could anyone help me? Thank you! That's the code:
syms u(x) d
a=0.1
Du=diff(u,x)
D2u=diff(u,x,2)
D3u=diff(u,x,3)
ode=diff(u,x,4)==-4*(a^4)*u
c1=u(0)==d
c2=D2u(0)==0
c3=D2u(1)==0
c4=D3u(1)==0
conds=[c1 c2 c3 c4]
usol(x)=dsolve(ode,conds)
usol(x)=subs(usol(x))
fplot(usol(x));
-------------------------------
I report also the error:
Error using fplot>singleFplot (line 240)
Input must be a function or functions of a single
variable.
Error in
fplot>@(f)singleFplot(cax,{f},limits,extraOpts,args)
(line 200)
hObj = cellfun(@(f)
singleFplot(cax,{f},limits,extraOpts,args),fn{1},'UniformOutput',false);
Error in fplot>vectorizeFplot (line 200)
hObj = cellfun(@(f)
singleFplot(cax,{f},limits,extraOpts,args),fn{1},'UniformOutput',false);
Error in fplot (line 166)
hObj =
vectorizeFplot(cax,fn,limits,extraOpts,args);
Error in fourhordertravesuoloelastico (line 18)
fplot(usol(x));

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回答（1 个）

David Jacob
David Jacob 2021-3-8
The line usol(x) = subs(usol(x)) isn't doing anything. The function fplot can't plot your function your function, because it is dependent on x and d. Give d a value and it will work. Put something like: subs(usol,d,value)

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