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Question: ODE odetest not returning zero – possible mistake?

Question:ODE odetest not returning zero – possible mistake?

salim-barzani 1555 Maple 2024
ode assumptions differential-equations odetest duplicate-question
May 01 2025
3

Why doesn't this ODE return zero when using odetest? Did I do something wrong?

Would you like help checking the equation or debugging the issue?

> 

restart
> 

with(PDEtools)
> 

declare(P(mu))

P(mu)*`will now be displayed as`*P

 (1)
> 

assume(A::real, r::real, rho::real, lambda::real)
> 

Psol := P(mu) = 2*A*lambda/((A^2+r)*exp(lambda*rho*mu)+r*exp(-lambda*rho*mu))

P(mu) = 2*A*lambda/((A^2+r)*exp(lambda*rho*mu)+r*exp(-lambda*rho*mu))

 (2)
> 

ode := (diff(P(mu), mu))^2-rho^2*P(mu)^2*(1+r*P(mu)^2) = 0

(diff(P(mu), mu))^2-rho^2*P(mu)^2*(1+r*P(mu)^2) = 0

 (3)
> 

res := odetest(Psol, ode)

4*A^6*rho^2*lambda^4*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4+8*r*A^4*rho^2*lambda^4*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-24*A^4*lambda^4*rho^2*exp(4*lambda*rho*mu)*r/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-4*A^6*rho^2*lambda^2*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4+4*A^2*r^2*rho^2*lambda^4*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-8*A^2*lambda^4*rho^2*exp(4*lambda*rho*mu)*r^2/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4+4*A^2*r^2*rho^2*lambda^4*exp(2*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-8*r*A^4*rho^2*lambda^2*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-8*A^4*lambda^2*rho^2*exp(4*lambda*rho*mu)*r/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-4*A^2*r^2*rho^2*lambda^2*exp(6*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-8*A^2*lambda^2*rho^2*exp(4*lambda*rho*mu)*r^2/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4-4*A^2*r^2*rho^2*lambda^2*exp(2*lambda*rho*mu)/(A^2*exp(2*lambda*rho*mu)+exp(2*lambda*rho*mu)*r+r)^4

 (4)
> 

simplify(res)

4*lambda^2*exp(2*lambda*rho*mu)*(((-2*lambda^2-2)*r^2+(-6*lambda^2-2)*A^2*r)*exp(2*lambda*rho*mu)+(lambda+1)*((A^2+r)^2*exp(4*lambda*rho*mu)+r^2)*(lambda-1))*A^2*rho^2/((A^2+r)*exp(2*lambda*rho*mu)+r)^4

 (5)
> 

P_hyper := P(mu) = 2*A*lambda/((A^2+r)*cosh(rho*mu)+(A^2-r)*sinh(rho*mu))

P(mu) = 2*A*lambda/((A^2+r)*cosh(rho*mu)+(A^2-r)*sinh(rho*mu))

 (6)
> 

res_hyper := simplify(odetest(P_hyper, ode), symbolic)

-16*A^4*lambda^2*rho^2*r*(lambda^2+1)/((A^2+r)*cosh(rho*mu)+(A^2-r)*sinh(rho*mu))^4

 (7)
 

NULL

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