Re: NonlinearModelFit: Freezing parameters

• To: mathgroup at smc.vnet.net
• Subject: [mg117515] Re: NonlinearModelFit: Freezing parameters
• From: dg <davide.guarisco at gmail.com>
• Date: Mon, 21 Mar 2011 06:16:19 -0500 (EST)
• References: <im201l\$tl\$1@smc.vnet.net> <im4iru\$d29\$1@smc.vnet.net>

```On Mar 20, 2:54 am, Peter Pein <pet... at dordos.net> wrote:

>
> Hi,
>
> you can wrap a Block[] around the call to NonlinearModelFit (NMF). You
> just have to change the way how the parameters are given to NMF using
> Variables:
>
> In[1]:= model=a0+a1 x+a2 x^2;
> data=Table[{x,.25+x^(3/2)},{x,0,2,1/3}];
>
> the normal call to NMF:
> In[3]:= f0=NonlinearModelFit[data,model,Variables[{a0,a1,a2}],x]//Normal
> Out[3]= 0.22546 + 0.601959 x + 0.416822 x^2
>
> Say you knew a0=1/4:
>
> In[4]:= f1=Block[{a0=.25},
> NonlinearModelFit[data,model,Variables[{a0,a1,a2}],x]//Normal
> ]
> Out[4]= 0.25 + 0.557096 x + 0.434077 x^2
>
> hth,
> Peter

Peter,
that's a neat trick. I think this does not work with models that are
not polynomials. For example, model= c0*Sin[c1*x].

```

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