Can AIC be used to compare a model with exponential smoothing with linear regressions?
I am doing some forecasting in R using Rob Hyndman's forecast package. The paper belonging to the package can be found .  In the paper, after explaining the automatic forecasting algorithms, the authors implement the algorithms on the same data set. However, after estimating both an exponential smoothing and ARIMA model they make a statement I do no understand (on page 17):     Note that the information criteria are not comparable.    I thought that an advantage of using AIC for model selection is that we can compare AIC values from different models, as long as they are estimated using the same data set. Is this incorrect?  This matter is of particular interest to me, as I was planning on combining forecasts from different model classes (e.g. exponential smoothing and ARIMA) using so called Akaike weights (see Burnham and Anderson, 2002, for discussion on Akaike weights)  References   Burnham, K. P., &amp; Anderson, D. R. (2002). Model selection and multi-model inference: a practical information-theoretic approach. Springer Verlag.
Where to say thanks? Where is the right place to say "thanks" to all those that answered my question? In a comment to my original post, or in a comment to the latest answer or where? The paradox:    We have a circle and there is another circle with smaller radius. They are co-centeric.  If circle make full turn without sliding, both smaller and bigger circle make full turn too. If we assume that the passed road is equal to the circumference of circles. We have got smaller circle's radius is equal to bigger one's.  Unsatisfying Solutions I found:    "Do not assume that smaller circle's circumference is equal to passed road since the surface that contacts to the ground is bigger one. " // Okey but it does not explain the paradox, it explains just what is the wrong assumption (even does not explain why it is a wrong assumption.) It is undeniable that every point on both smaller and bigger circle will contact exactly one and only one point on their path. Therefore we can think that this is a bijective maps and smaller circle is isomorphic to bigger one. (Okey but ....)   Question: What is the true answer? What is wrong with the definition of circumference of a circle and relationship with its taken path. Negative R squared contradicts ssa/sst? What can you use Python generator functions for? I'm starting to learn Python and I've come across generator functions, those that have a yield statement in them.  I want to know what types of problems that these functions are really good at solving. 32-bit, 64-bit CPU op-mode on Linux I'm confused. Running Fedora Linux, lscpu yields:  Architecture:            i686 CPU op-mode(s):          32-bit, 64-bit ...   But when I try to install a 64-bit program (Chrome) I get error like:     Package /....x86_64.rpm has incompatible architecture x86_64. Valid architectures are ['i686', 'i586', 'i486', i386']   I'm less interested in being able to install Chrome and more interested in why lscpu says that my CPU can run in 64-bit mode; clearly this can't mean I can run 64-bit programs. Can anyone clarify? What is the difference between Θ(n) and O(n)? Sometimes I see Θ(n) with the strange Θ symbol with something in the middle of it, and sometimes just O(n). Is it just laziness of typing because nobody knows how to type this symbol, or does it mean something different? PDF editing within Apex/Visualforce ID a book about a mirror world and 4th dimension I read a book about 10-15 years ago about a boy and a girl who find a mirror. What made the mirror special was, they were able to enter the reflection and be a part of the reverse image world. They end up going to school and when asked to write something on the board, it ends up being backwards, but to them looks normal.  Later, the two end up in a world with 4 dimensions. With the added dimension they can't see as they normally could. If one moved a certain way the other would see their insides. Eventually a native of that dimension made some type of device that lets them see regularly.  Other than that my memory is blank. If I remember anything else I will be sure to edit it in. I am currently reading Murphy's ML: A Probabilistic Perspective. In CH 3 he explains that a batch update of the posterior is equivalent to a sequential update of the posterior, and I am trying to understand this in the context of his example.  Suppose $D_a$ and $D_b$ are two data sets and $\theta$ is the parameter to our model. We are trying to update the posterior $P(\theta \mid D_a, D_b)$. In a sequential update, he states that, $$ (1) \ \ \ \ \ \ \ \  P(\theta \mid D_{a}, D_{b}) \propto P(D_b \mid \theta) P(\theta \mid D_a) $$ However, I am slightly confused as to how he got this mathematically. Conceptually, I understand that he is saying the posterior $P(\theta \mid D_a)$ is now a prior used to update the new posterior, which includes the new data $D_b$, and is multiplying this prior with the likelihood $P(D_b \mid \theta)$. Expanding the last statement out, I have, $$  P(D_b \mid \theta) P(\theta \mid D_a) = P(D_b \mid \theta) P(D_a \mid \theta) P(\theta) $$  but are we allowed to say $P(D_a \mid \theta) P(D_b \mid \theta) = P(D_a, D_b \mid \theta)$ in order to make the connection in (1)? How do I assign a value to a whole array of integers? How can I retain HTML form field values in JSP after submitting form to Servlet? Why would layout_width="wrap_content" take up the entire width of the screen? ant deploy error - Maximum size of request reached I used to deploy metadata using ant migration tool successfully but from last night I am getting the below error:  John@John:~/mm_workspace/TEST_Project/deploy$ ant deployUnpackaged  Buildfile: /home/john/mm_workspace/TEST_Project/deploy/build.xml  deployUnpackaged:  BUILD FAILED /home/john/mm_workspace/TEST_Project/deploy/build.xml:72: Failed to submit request to https://cs19.salesforce.com/services/Soap/m/35.0/00D293456000Qaf for user john@test.com.dev. Error: {http://schemas.xmlsoap.org/soap/envelope/}Client - Maximum size of request reached. Maximum size of request is 52428800 bytes.  Total time: 2 minutes 10 seconds   I think this is because of too much metadata that I am trying to deploy. For now, I am deploying classes and then VF pages and so on but I am looking for an option to deploy everything in one go without running into the above error.  I am sure that people are working on more complex projects than mine with lots of metadata and I am wondering how are they deploying with out hitting this error?  Thanks Vandermonde identity corollary $\sum_{v=0}^{n}\frac{(2n)!}{(v!)^2(n-v)!^2}={2n \choose n}^2$ I am trying to prove this identity:  $$\sum_{v=0}^{n}\frac{(2n)!}{(v!)^2(n-v)!^2}={2n \choose n}^2$$ I think this identity (corollary of Vandermonde identity): $${n\choose 0}^2+{n\choose 1}^2+{n\choose 2}^2+\cdots+{n\choose n}^2={2n \choose n}$$ is applicable for solving it. Please give me some hints. thank you Western Digital drive making beeping noise Skipping Iterations in Python I have a loop going, but there is the possibility for exceptions to be raised inside the loop. This of course would stop my program all together. To prevent that I catch the exceptions and handle them. But then the rest of the iteration runs even though an exception occurred. Is there a keyword to use in my except: clause to just skip the rest of the current iteration? It is currently said that MD5 is partially unsafe. Taking this into consideration, I'd like to know which mechanism to use for password protection.  This question,   suggests that hashing multiple times may be a good idea, whereas  suggests using salt.  I'm using PHP. I want a safe and fast password encryption system. Hashing a password a million times may be safer, but also slower. How to achieve a good balance between speed and safety? Also, I'd prefer the result to have a constant number of characters.   The hashing mechanism must be available in PHP It must be safe It can use salt (in this case, are all salts equally good? Is there any way to generate good salts?)   Also, should I store two fields in the database (one using MD5 and another one using SHA, for example)? Would it make it safer or unsafer?  In case I wasn't clear enough, I want to know which hashing function(s) to use and how to pick a good salt in order to have a safe and fast password protection mechanism.  Related questions that don't quite cover my question: What happens when the Runner stack is empty? When the corporation R&amp;D is empty the corporation loses.  What happens when the Runner's stack is empty?    I think that: He must finish the game with only the cards on the table.  or  I doubt that: He reshuffles the heap into a new stack. Given complex $|z_{1}| = 2\;\;,|z_{2}| = 3\;\;, |z_{3}| = 4\;\;$ : when and what is $\max$ of $|z_{1}-z_{2}|^2+|z_{2}-z_{3}|^2+|z_{3}-z_{1}|^2$ How to boot from iso with Grub2/Burg boot loader