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From: "pietro " <bracardi82@email.it>
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Subject: problem using resid
Date: Wed, 27 May 2009 14:36:03 +0000 (UTC)
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Hi,

i have to validate a estimated arx model. I try to use resid command but it gives me the following error:

the resid returns me the following error:

??? Error using ==> utresid at 199
Resid cannot be applied to Continuous Time data.

Error in ==> idmodel.resid at 54
    utresid(v{:});

I use resid command in this way:

hpidfrd=idfrd(hp,2*pi*fp,0);
modarx=arx(hpidfrd,[num+1 den])
resid(hpidfrdiddata,modarx) 

fp: frequency value 
hp: complex transfer function value 
num e den: arx model orders

How can i perform a residual analysis with Continuous Time data?