Hello,

I'm sorry to bother you but I have a problem with the numeric resolution of a system of 3 differential equations. The system is as follows  : sysdif :=

As you can see the system is composed of 3 differential equations, and I enter initial conditions in the object "sysd". Then I try a numeric resolution by executing the following command (I give a value to parameters before)  :

Then Maple's answer is : Error, (in dsolve/numeric/process_input) missing differential equations and initial or boundary conditions in the first argument: sysdif.

I can't see where I'm wrong, does anyone notice something that could explain this error message ? There's no help page about this error so I ask the question here.

Thank you very much for your time if you answer this,

Louis

Hi guys,

I'm studying a system of six differential equations. Given the fact that the system cannot be solved symbolically, I've tried the numeric procedure, and it works. I proceeded like this :

soleqd:=dsolve(sysd2,numeric,var);

then i checked if maple could calculate the solutions for given values of t. It works for t=0, t=0.5, t=1,t=2,...,t=5. The solutions are all real numbers.

But when i try to draw a graphic representation of the solutions, it doesn't work. I do :

ff1:=t->subs(soleqd(t),u[1](t));
gg1:=t->subs(soleqd(t),nu[1](t));

Then :

plot(['ff1(t)','gg1(t)',t=0..5],u[1]=0...1,nu[1]=0...1);

(The square brackets are indices)

Now maple answers that it is "unable to evaluate the function to numeric values in the region". I went to the help page but no solution seems to work. I can't figure it out by myself. Does anybody notice something wrong with my code ?

Thank you for your time,

Best regards,

Louis

Hi guys,

I'm trying to draw a phase portrait based on a system of differential equations, but executing the DEplot command gives me the response in the title. 

The command I entered is this one :

DEplot(sysdif,[u(t),nu(t)],t=0..50,{[u(0)=0.831,nu(0)=0.7]},linecolor=red,numpoints=1000, thickness=1, u=0.5...1, nu=0.6...1, color=black);

the system of equation is this one :

eqd1 := diff(u(t), t) = u(t)*[-gamma + (rho)/(mu - nu(t)) - delta*u(t) + pii - (tau)/(alpha + epsilon*exp(-beta*((omega-u(t))/(kappa-u(t)))))] ;
eqd2 := diff(nu(t), t) = nu(t)*[(omega-u(t))/(kappa-u(t)) - (tau)/(alpha+epsilon*exp(-beta*((omega-u(t))/(kappa-u(t)))))] ;

the model is calibrated. I understand that maple cannot store a kind of number but even changing the parameters won't help. I've been looking for people with same error message but using solutions provided by forum members don't work. Before getting that error message i did have the one with "vars must be declared as a list ..." so I did :

u:='u' ;

nu:='nu';

but now I have the error  "unable to store  '[HFloat(0.005711776872341132)]' when datatype=float[8]".

Does anybody have an idea of the solution to my problem ?

Thanks for your time,

best regards,

Louis