       Re: help plot log[f[t]] vs a parameter using an ODE

• To: mathgroup at smc.vnet.net
• Subject: [mg81184] Re: help plot log[f[t]] vs a parameter using an ODE
• From: j.f.b.payne at tesco.net
• Date: Fri, 14 Sep 2007 03:50:30 -0400 (EDT)
• References: <fc85qt\$liu\$1@smc.vnet.net><fcb42d\$fmp\$1@smc.vnet.net>

```Maybe what is wanted is a 3D plot of the solution to the differential
equation, as a function of the dependent variable `t' and the
parameter `a'

In which case, a perhaps inelegant approach is

tbl=Table[{a,y[t] /. First@First@NDSolve[{y'[t] == a (y[t]/((y[t])^2 +
b )) - c y[t] + d /. {d -> 0.1 , c -> 1 , b -> 10 },y==0},y,{t,
0,200}]},{a,5,40,5}]

fn[tt_,a_]:=Interpolation[tbl /. t->tt][a]

Plot3D[fn[t,a],{t,0,200},{a,5,40}]

or

Plot3D[Log[fn[t,a] ],{t,0,200},{a,10,40}]

if the Log is wanted, but there seem to be negative values so this
makes error messages
(I don't have time to look into this)

Regards

John Payne

```

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