@sarra 

One again, thank you for all remarks.
I found how can I add legend. Thank you.

http://www.mapleprimes.com/questions/149585-How-To-Order-Legend-Of-Multiple-Plots

@tomleslie 

thank you very much for your answer.

I tried to add a legend but the command legend does not work with dispaly..

Can we add legend.

@acer 

Thank you very much for your answer.

It's a nice ansewer, when i am tried to use plot(y, x=1000..1001), there is no display, i think because we have a very smal values of y in this prescripted interval.... Maybe I am sure.

What I would like to do: is to solve the ode:

ode := diff(y(x), x, x) = x*y(x)+(16/51)*x^(17/12);

with boundary condition

ics:=y(1000)=0, y(1001)=1;

z=dsolve({ics, ode});

now, I would like to plot the solution obatained : plot(z,x=1000..1001);

then i plot the error between my function y and z in the same interval.

error=z-y;

and plot(error, x=1000..1001); but in both case there is no desplay

Thank for helping me.

Thank you for your answer.

I agree with you, one can use

P :=x^6-4*x^3+x-2;
S := sturmseq(P,x);
to get the sturm sequence.

Please, have you an idea how to give an ansewer of the rest of my question.

thanks

@tomleslie 

thank you for the idea.

@Kitonum 

Thank you very much

Okay, I fixed the error,  change P to P(t) and N to N(t) in the system.

and we change q1=0.5 to q1:=0.5, now the code will run.

@Kitonum 

First, thank you for your answer.

The matrix obtained  not square matrix,  there is a problem I think in index of i=1..N, or something else.  I knox that I must find a square Matrix but where i the mistake.

Thanks one again.

@Kitonum 

Thank you very much, that's I mean.

@Preben Alsholm 

Thank you very much for your answer.

@Kitonum 

thanj you very much.

@Kitonum 

Thank you very much for the idea. 

I do the same calculs without maple i get the same solution, but three page of computation, to get the same result, so thanks for you and for maple.

Please, how can I sketch the phase portrait.

@Carl Love 

Thank you very much for the idea. 

I do the same calculs without maple i get the same solution, but three page of computation, to get the same result, so thanks for you and for maple.

Please, how can I sketch the phase portrait.

@Kitonum 

Thank you very much for answer, I understand what yoy say.

Can we show in the picture the  existance of stability of equilibria.

Thank you one again.

@Carl Love 

Than you very much for the answer