dx1/dt = (-p1*km*x1 - p1*x1^2 + km*u1 - x1*vm + x1*u1) / (km + x1);
dx2/dt = -p2*x2 + p1*x1;
dx3/dt = p2*x2 - x3*p3;
dx4/dt = x3*p3 - x4*p4;
dx5/dt = -p5*x5 + x4*p4;
dx6/dt = -p6*x6 + p5*x5;
dx7/dt = -p7*x7 + p6*x6;
dx8/dt = p7*x7 - p8*x8;
dx9/dt = -x9*p9 + p8*x8;
dx10/dt = x9*p9 - x10*p10;
dx11/dt = x10*p10 - x11*p11;
dx12/dt = x11*p11 - p12*x12;
dx13/dt = -x13*p13 + p12*x12;
dx14/dt = x13*p13 - p14*x14;
dx15/dt = -p15*x15 + p14*x14;
dx16/dt = p15*x15 - x16*p16;
dx17/dt = -p17*x17 + x16*p16;
dx18/dt = -p18*x18 + p17*x17;
dx19/dt = -x19*p19 + p18*x18;
dx20/dt = -p20*x20 + x19*p19;
y1 = x1;
y2 = x2;
y3 = x3;
y4 = x4;
y5 = x5;
y6 = x6;
y7 = x7;
y8 = x8;
y9 = x9;
y10 = x10;
y11 = x11;
y12 = x12;
y13 = x13;
y14 = x14;
y15 = x15;
y16 = x16;
y17 = x17;
y18 = x18;
y19 = x19;
y20 = x20
