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These are questions asked by sarra


I need you help to understand this problem.


Let alpha=0.1.;

When I do :  (-0.2)^alpha I get a complex number.


I must find a real number.

What's the problem

Thanks for your idea.


Dear all;

nice to speak with you.

complete a table randomly by positive three-digit numbers and display only the symmetrical numbers.



Dear all;

I need your help to display the value of phi[jj] in the following loop. 


for jj from 1 by 1 to 2 do
end do;


but the index jj in the integral does not change. I have any idea what is the problem. 

Thank you very much for your help. 



Dear All,

I need your help to plot the phase portrait using DEtools[DEplot]  these are the lines of the code. But when I make RUN, there is an error. I need your help to fix the error. Many thinks.


r1:=1; r2:=1; q2:=2; q1=0.5;  a1:=1;

Sys1 := {diff(N(t),t) = r1*N*(1-N/q1)-P*N/(1+N), diff(P(t),t) = r2*P*(exp(-a1*P)-q2)+P*N/(1+N)};



Many thinks

Dear all;

I need your help to get all the solution of this nonlinear  system  with four parameters: r1, r2, q1, q2  assumed to be positives. Let the system:

the first equation is: r1*x*(1-x/q1)=x*y/(1+x)

the second equation: r2*y*(exp(-y)-q2)=-x*y/(1+x)

How can get the positive solution ( x, y) of the previous system.

Thank you for your help.

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