diff: variable must not be a number; found: | bug??
Subject: diff: variable must not be a number; found: | bug??
From: Evan Cooch
Date: Mon, 18 Nov 2013 12:59:08 -0500
Thanks very much for the additional clarification.
On 11/18/2013 12:48 PM, Robert Dodier wrote:
> On 2013-11-18, Evan Cooch <evan.cooch at gmail.com> wrote:
>
>> Need to add the following:
>>
>> lls_sigma1 :
>> subst([s_0=0.35,s_1=0.60,s_2=0.80,s_3=0.90,m_3=1.25,lambda=1.08,sigma_1=0,sigma_2=0],rhs(first(lls_sigma1));
>>
>> For some strange reason, I don't always need to do this. But, as soon as
>> I add the rhs(first(<whatever I set the implicit deriv to>)), works fine.
> Well, 'subst' doesn't pay attention to the special role of the variables
> in a derivative, which leads to the "can't differentiate wrt a number"
> message. 'at' is just like subst except that it treats variables in a
> derivative differently (also, iirc, integrals & summations). For those,
> it yields a noun expression.
>
> If you omit the rhs(first(lls_sigma1)) you get something like the
> following from 'at':
>
> ['at('diff(...., sigma_1), [sigma_1=..., ...]) = <some number>]
>
> best
>
> Robert Dodier
>
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