# a biochemical switch
# x + x  --> 3x  at a rate K=K0/(K1+x^2)
# x --> product  at rate K2
# b --> x   transient stimulus
x'=-k2*x+b*s(t)+k0*x*x/(K1+x^2)
par k0=2.5,k1=1,k2=1,b=.3,ton=20,toff=25
s(t)=heav(t-ton)*heav(toff-t)
@ xhi=100,total=100,ylo=-.1,yhi=1.5
done