Hello,

I think, in the following example the NonNegative option is ignored 
during integration, because Y contains negative values.

I would be glad if somebody could confirm this or provide me with an 
explanation.

Best regards,
Simon


Y0 = [2.4088e+11, 0, 0]
TSPAN = [0.0, 24.0];
vopt = odeset ('NonNegative', [1,2,3]);
[T,Y] = ode45(@ODEs, TSPAN, Y0, vopt);


function yprime = ODEs(T,Y)

     # constants
     a = 4.0  * 10-6;
     b = 2.1  * 10-12;
     c = 2.5  * 105;
     d = 1.0  * 10-5;
     e = 6.5  * 10-2;
     f = e /100;
     g = 7.2  * 10-3;

     # first-order-ODEs
     yprime = [

         - d   * Y(1) * c;

           d   * Y(1) * a / b ...
         + f   * Y(3) ...
         - e    * Y(2);

           e    * Y(2) ...
         - f   * Y(3) ...
         - g   * Y(3);
     ];

endfunction


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