kill(a,b,c,d)$
solve([(a-b*P)*N=0,P*(c*N-d)=0],[N,P]);

a: 1.1$ 
b: 0.4$
c:0.1$
d:0.4$
N0: d/c;
P0: a/b;

/*PARAMETAR A*/
for i:1 thru 20 do (a:0.1*i+0.2, display(a),
    rj: rk([(a-b*P)*N,P*(c*N-d)],[N,P],[N0,P0],[t,0,50,0.01]),
    rjN[i]: makelist([f[1],f[2]],f,rj),
    rjP[i]: makelist([f[1],f[3]],f,rj)
)$
with_slider(
   i,makelist(i,i,1,20,1),
   [[discrete,rjN[i]],[discrete,rjP[i]]],[y,0,10],[legend,"N","P"]
)$

a: 1.1$ 
b: 0.4$
c:0.1$
d:0.4$
N0: d/c;
P0: a/b;

/*PARAMETAR B*/
for i:1 thru 20 do (b:0.05*i+0.05, display(b),
    rj: rk([(a-b*P)*N,P*(c*N-d)],[N,P],[N0,P0],[t,0,50,0.01]),
    rjN[i]: makelist([f[1],f[2]],f,rj),
    rjP[i]: makelist([f[1],f[3]],f,rj)
)$
with_slider(
   i,makelist(i,i,1,20,1),
   [[discrete,rjN[i]],[discrete,rjP[i]]],[y,0,20],[legend,"N","P"]
)$

a: 1.1$ 
b: 0.4$
c:0.1$
d:0.4$
N0: d/c;
P0: a/b;

/*PARAMETAR C*/
for i:1 thru 20 do (c:0.01*i+0.03, display(c),
    rj: rk([(a-b*P)*N,P*(c*N-d)],[N,P],[N0,P0],[t,0,50,0.01]),
    rjN[i]: makelist([f[1],f[2]],f,rj),
    rjP[i]: makelist([f[1],f[3]],f,rj)
)$
with_slider(
   i,makelist(i,i,1,20,1),
   [[discrete,rjN[i]],[discrete,rjP[i]]],[y,0,10],[legend,"N","P"]
)$

a: 1.1$ 
b: 0.4$
c:0.1$
d:0.4$
N0: d/c;
P0: a/b;

/*PARAMETAR D*/
for i:1 thru 20 do (d:0.075*i+0.1, display(d),
    rj: rk([(a-b*P)*N,P*(c*N-d)],[N,P],[N0,P0],[t,0,50,0.01]),
    rjN[i]: makelist([f[1],f[2]],f,rj),
    rjP[i]: makelist([f[1],f[3]],f,rj)
)$
with_slider(
   i,makelist(i,i,1,20,1),
   [[discrete,rjN[i]],[discrete,rjP[i]]],[y,0,10],[legend,"N","P"]
)$