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) -- To reply via email subtract one hundred and four