Dsolve generates result with variable "t" when t not used

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Sergio Manzetti 2017-10-2

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https://ww2.mathworks.cn/matlabcentral/answers/359302-dsolve-generates-result-with-variable-t-when-t-not-used

评论： Chandani Madnani 2017-10-4

Hi; I tried to solve a PDE using dsolve, and the code looks like:

if true
syms h r l
h = 2
g = 5
dsolve('r^2*(h^2*(D2v+1/r*v+2*i*h*Dv))-l*2*i*h*v=0','v(0)=r')
end

however, the results is strange and has t in it as variable:

C15*exp(-(t*((h*(h^3*i^2*r^2 - h*r + 2*l*i))^(1/2) + h^2*i*r))/(h*r)) - exp((t*((h*(h^3*i^2*r^2 - h*r + 2*l*i))^(1/2) - h^2*i*r))/(h*r))*(C15 - cos(r))

Can someone point to the reason for this "t" variable?

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Torsten 2017-10-4

http://www.wolframalpha.com/input/?i=v''(r)%2B1%2Fr*v(r)%2B2*I*C*v'(r)-2*I*B*v(r)%2Fr%5E2%3D0

Best wishes

Torsten.

Chandani Madnani 2017-10-4

What is h and g? Are they representing constants B and C from the mathematical equation? Why is h and l used inside 'dsolve' then? What is 'i' in the equation for? Is that also a constant?

For more details about using "dsolve", please see the documentation link below:

https://www.mathworks.com/help/symbolic/dsolve.html

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