Jim Clark wrote:
> The reference manual shows the following example for the gradient()
> function:
>
> sage: x,y = var('x y')
> sage: f = x^2+y^2
> sage: f.gradient()
> (2*x, 2*y)
>
> However, if instead I enter:
>
> sage: x,y,n = var('x y n')
> sage: f = x^n+y^n
> sage: f.gradient()
> (y^n*log(y) + x^n*log(x), n*x^(n - 1), n*y^(n - 1))
>
> (not what I wanted, but I can understand what happened.)
> So I tried:
>
> sage: f(x,y) = x^n+y^n
> sage: f.gradient()
> ((x, y) |--> y^n*log(y) + x^n*log(x), (x, y) |--> n*x^(n - 1), (x, y)
> |--> n*y^(n - 1))
>
> So even if I specify that f is a function of x and y,
> gradient() still insists on also differentiating w.r.t. n
>
> How do I tell gradient() that n is a constant?
Good point. Right now, the gradient function looks like this:
from sage.modules.free_module_element import vector
l=[self.derivative(x) for x in self.variables()]
return vector(l)
That second line should probably be
l=[self.derivative(x) for x in self.arguments()]
and then your last example should work.
Jason
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