Maybe this will work
%start and initialize values
for D=D0:DD:Dmax %it stops when D>Dmax %in W
B=Bi;S=Si;
Y=0;
while 1 %in Z
u=umax*S/(Ks+S);
if (abs(u-D)<=0.01)
B0=D*B;
%print B0, S,B,D
D=D+DD;
break %return from the while loop
else
Y=Y+1;
if Y>50
B0=D*B;
%print B0, S,B,D
D=D+DD;
break %return from the while loop
else
%define new delta B
%define new delta S
%update B
%update S
end
end
end
end
