Ah! Thank you. I had not heard of closure before. Now, I have heard of it,
but am not sure if I can completely understand it! I guess this might be
worth being explained in the manual. One thing that is still kind of
confusing is that in your example, z is defined after the closure is
created until the end of that iteration. So, z is printed once below, but
not the second time in the beginning of the second iteration!
julia> for i=1:10
if i>=2; println(z); end
z=2
g()=2z
println(z)
end
2
ERROR: z not defined
in anonymous at no file:2
On Tuesday, April 28, 2015 at 10:17:17 PM UTC-4, Avik Sengupta wrote:
> Yes, sorry I jumped the gun. Thanks for clarifying.
>
> But it still does not have anything to do with Optim :)
>
> The problem is due to defining an inline function (line 43) that creates
> closure over the "x_previous" variable. To test this, just comment that
> line (and adjust the Optim.optimize call), the problem goes away.
>
> A simpler version of the code that fails is as follows:
>
> julia> function f()
> for i=1:10
> if i>2; println(z); end
> z=2
> g() = 2z
> end
> end
> f (generic function with 1 method)
>
> julia> f()
> ERROR: z not defined
> in f at none:3
>
> A fix to get it to work is to declare the variable at the start of your
> function. Similarly, adding a "local x_previous" at the top of your
> function makes it work correctly. Remember, variables in Julia are lexical
> in scope.
>
> julia> function f()
> local z
> for i=1:10
> if i>2; println(z); end
> z=2
> g()=2z
> end
> end
> f (generic function with 1 method)
>
> julia> f()
> 2
> 2
> 2
> 2
> 2
> 2
> 2
> 2
>
>
> On Wednesday, 29 April 2015 02:23:28 UTC+1, Pooya wrote:
>>
>> If you comment out lines 42-49, you will see that it works fine!
>>
>> On Tuesday, April 28, 2015 at 9:20:49 PM UTC-4, Pooya wrote:
>>>
>>> Thanks, but I think "if iter > 2" (line 21) makes sure that x_previous
>>> is defined in the previous iteration. Just to be clear, the condition to
>>> check here was "g_norm > g_norm_old", but I changed it to get there as
>>> early as the second iteration.
>>>
>>> On Tuesday, April 28, 2015 at 9:13:49 PM UTC-4, Avik Sengupta wrote:
>>>>
>>>> I'm seeing the error in line 22 of your gist where you are trying to
>>>> print the current value of "x_previous". However, x_previous is first
>>>> defined in line 38 of your gist, and so the error is correct and doesnt
>>>> have anything to do with Optim, as far as I can see.
>>>>
>>>> On Wednesday, 29 April 2015 01:39:02 UTC+1, Pooya wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I have a problem that has made me scratch my head for many hours now!
>>>>> It might be something obvious that I am missing. I have a Newton-Raphson
>>>>> code to solve a system of nonlinear equations. The error that I get here
>>>>> does not have anything to do with the algorithm, but just to be clear, I
>>>>> need to find the best possible solution if the equations are not
>>>>> solvable,
>>>>> so I am trying to stop simulation when the direction found by
>>>>> Newton-Raphson is not correct! In order to do that I put an if-loop in
>>>>> the
>>>>> beginning of the main loop to take x from the previous iteration
>>>>> (x_previous), but I get x_previous not defined! I am using the Optim
>>>>> package to do a line search after the direction has been found by
>>>>> Newton-Raphson. If Optim is not used, things work perfectly (I tried by
>>>>> commenting out those lines of code). Otherwise I get the error I
>>>>> mentioned.
>>>>> My code is here:
>>>>> https://gist.github.com/prezaei85/372bde76012472865a94, which solves
>>>>> a simple one-variable quadratic equation. Any thoughts are very much
>>>>> appreciated.
>>>>>
>>>>> Thanks,
>>>>> Pooya
>>>>>
>>>>
