I believe we can make a variable transform and then apply the derivative
using the expression converted to a variable, like:
x = a**2 + c + d**3
x.diff((a + c**2))
changing variables:
v = a + c**2
a = v - c**2
c = (v-a)**0.5
the new x will be:
x2 = (v-c**2)**2 + (v-a)**0.5 + d**3
and the derivative could be computed as:
x2.diff(v)
is that reasonable?
2013/11/2 F. B. <[email protected]>
>
>
> On Saturday, November 2, 2013 12:23:00 AM UTC+1, brombo wrote:
>>
>> Consider Lagrangian field theory where the derivatives are taken with
>> respect to the gradient of a field. In the case of quantum electrodynamics
>> with respect to the gradient of a spinor field.
>>
>
> Yes, that would be needed. I am wondering, is there a generic algorithm
> for functional derivatives, or is it more likely to be a complicated matter?
>
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