Now how do I evaluate f itself at those same points. I can't seem to
figure it out.
On Sep 24, 9:47 pm, Jason Grout <jason-s...@creativetrax.com> wrote:
> Sterling wrote:
> > How do I evaluate a Jacobian at certain values? For example, I type:
>
> > x1,x2,x3 = var('x1 x2 x3')
>
> > f1(x1,x2,x3) = 3*x1 - cos(x2*x3) - (1/2)
> > f2(x1,x2,x3) = x1^2 - 81*(x2 + 0.1)^2 + sin(x3) + 1.06
> > f3(x1,x2,x3) = e^(-x1*x2) + 20*x3 + (10*pi - 3)/3
>
> > f = (f1,f2,f3)
>
> > j = jacobian(f, [x1,x2,x3])
>
> > I thought it would (intuitively) be:
>
> > j(x1=0.1,x2=0.1,x3=-0.1)
>
> > But apparently not. Please advise.
>
> I think the thing I would do is make your f a symbolic expression by
> actually calling the functions with arguments:
>
> f = (f1(x1,x2,x3), f2(x1,x2,x3), f3(x1,x2,x3))
>
> Then things work like you wished.
>
> Another thing you could do is make the matrix explicitly a symbolic
> expression matrix:
>
> matrix(SR,j)
>
> Then your idea works great as well.
>
> Thanks,
>
> Jason
>
> --
> Jason Grout
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