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Re: Working with D, definition of a function
*To*: mathgroup at smc.vnet.net
*Subject*: [mg75979] Re: Working with D, definition of a function
*From*: Bill Rowe <readnewsciv at sbcglobal.net>
*Date*: Mon, 14 May 2007 03:45:02 -0400 (EDT)
On 5/13/07 at 5:46 AM, thomas.??? at balliol.ox.ac.uk (Thomas Schmelzer)
wrote:
>I have defined a map
>ComPath[w_, mu_, bias_] := mu*(\[ImaginaryI]*w + 1)^2 + bias; Now, I
>would like to use the derivative with respect to w as a further
>function.
>D[ComPath[w, mu, 0], w]
>gives the answer I expect, but
>ComPathPrime[w_, mu_] := D[ComPath[w, mu, 0], w];
>doesn't seem to make sense
>ComPathPrime[2, 1]
>results in
>General::ivar : 2 is not a valid variable.
Right.
Notice what you've asked Mathematica to do. That is you are
asking Mathematica to compute the derivative of -3 + 4 I (the
result returned by ComPath[2,1,0] with respect to 2 (the value
you gave w). So, it should be no surprise when Mathematica complains
Notice
In[16]:= ComPathPrime[w, 1]
Out[16]= 2*I*(I*w + 1)
Which is the same as
In[14]:= D[ComPath[w, mu, 0], w]
Out[14]= 2*I*mu*(I*w + 1)
So, it is clear ComPathPrime is working correctly
If you need ComPathPrime evaluated at a specific value for w
then do
In[14]:= D[ComPath[w, mu, 0], w]
Out[14]= 2*I*mu*(I*w + 1)
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