Originally Posted by

**laureanda** Hello,

this is the entire code:

> with(CurveFitting);

> with(plots);

> with(Optimization);

> F := diff(X(t), t) = X(t)*(A-B*Y(t));

> G := diff(Y(t), t) = Y(t)*(C*X(t)-E);

> f := diff(x(t), t) = x(t)*(a-b*y(t));

> g := diff(y(t), t) = y(t)*(c*x(t)-e);

>

>

> x0 := .4; y0 := .5; a := 1.8; b := .4; c := .2; e := .8;

0.4

0.5

1.8

0.4

0.2

0.8

> solnum := dsolve([f, g, x(0) = x0, y(0) = y0], [x(t), y(t)], numeric, range = 0 .. 10);

>

> h(t):=e log(x(t))- c x(t)- b y(t)+a log (y(t)) : ;

> plot(t, h);

Warning, unable to evaluate the function to numeric values in the region; see the plotting command's help page to ensure the calling sequence is correct

> H(t,A,B,C,E):=E log(x(t))- C x(t)- B y(t)+A log(y(t)) : ;

> Er(t,A,B,C,E,T):=1/(2)*(H(t,A,B,C,E) - T)^(2) ;

1 2

(t, A, B, C, E, T) -> - (H(t, A, B, C, E) - T)

2

> Er(t, a, b, c, e, 1);

1 2

- (0.8 ln(x(t)) - 0.2 x(t) - 0.4 y(t) + 1.8 ln(y(t)) - 1)

2

>

*****************************

Note: I have used 2 function (f and F, g and G) because I try to find the parameters a,b,c,e having only "solnum", like "experimental data", so f and g make the numerical solution, F and G have A,B,C,E unknown.