Is there any definition of the sum of $n$ summands, when $n$ is not a natural number?
How to extend summations to fractional orders?
Why do you need 2 resistors when hooking up a transistor as a switch What is the point of R2 in the following diagram:   I get that R1 controls the current to the Base, but what does R2 do? apt-get autoremove wants to remove linux headers Today I ran apt-get autoremove to remove un-needed packages and it wants to remove linux-headers-3.2.0-37 and linux-headers-3.2.0-37-generic  Reading package lists... Done Building dependency tree        Reading state information... Done The following packages will be REMOVED: libglademm-2.4-1c2a linux-headers-3.2.0-37 linux-headers-3.2.0-37-generic ttf-umefont    ttf-unfonts-core 0 upgraded, 0 newly installed, 5 to remove and 0 not upgraded. After this operation, 67.6 MB disk space will be freed. Do you want to continue [Y/n]?    Is it safe to remove these? My installed kernel is a newer version than the headers that autoremove lists.  uname -r 3.2.0-38-generic Possible Duplicate:                If in a multiple linear regression (enter method) the general model isn't significant (F>.05) but one of the predictors is significant (β&lt;.05), should I consider it as a significant result? Dealing with rust on a steel frame How to choose between learning algorithms I need to implement a program that will classify records into 2 categories (true/false) based on some training data, and I was wondering at which algorithm/methodology I should be looking at. There seem to be a lot of them to choose from -- Artificial Neural Network, Genetic Algorithm, Machine Learning, Bayesian Optimization etc. etc., and I wasn't sure where to start. So, my questions is:  How should I choose a learning algorithm I should use for my problem?  If this helps, here is the problem I need to solve.    The training data: The training data consists of many rows like this:    Precursor1, Precursor2, Boolean (true/false)   The run I will be given a bunch of precursors. Then,     I choose an algorithm A from different algorithms (or dynamically generate an algorithm), and apply it on every possible combinations of these precursors and collect the "record"s  that are emitted. The "record" consists of several key-value pairs*. I apply some awesome algorithm and classify these records in to 2 categories (true/false). I will generate a table that has the same format as the train data: Precursor1, Precursor2, Boolean   And the whole program is scored based on how many true/false I got right.  *:"Record"s will look like this (hope this makes sense)  Record         [1...*] Score -Precursor1             -Key -Precursor2             -Value   There are only a finite number of possible Keys. Records contain different subset of these keys (some records have key1, key2, key3... other records have key3, key4... etc.).  I actually need 2 learning. One is for step 1. I need to have a module that looks at the Precursor pairs etc. and decide what algorithm to apply in order to emit a record for the comparison. Another is for step 2. I need a module that analyzes the collection of records and categorize them into the 2 categories (true/false).    Thank you in advance! Skip empty rasters in ArcGIS I'm trying to write some code to skip over empty raster sets when converting rasters to point (the empty sets stop the conversion, leaving me with a half complete model run).  I know that I can identify empty rasters using the ALLNODATA result from "Get Raster Properties" .  I know I can delete rasters using the Delete.management tool.  I know I should be able to create a branch using calculate value.  But I'm inexperienced with python and modelbuilder, and haven't been able to put this all together. Could someone help me figure out what I am doing wrong? My code and an image of the modelbuilder setup are below.  def fn(Property):  #Import modules      import arcpy  #ifelse statement if Property == "1":             return "true" elif Property == "0":            return "false" Can grep output only specified groupings that match? Say I have a file:  # file: 'test.txt' foobar bash 1 bash foobar happy foobar   I only want to know what words appear after "foobar", so I can use this regex:  "foobar \(\w\+\)"   The parenthesis indicate that I have a special interest in the word right after foobar.  But when I do a grep "foobar \(\w\+\)" test.txt, I get the entire lines that match the entire regex, rather than just "the word after foobar":  foobar bash 1 foobar happy   I would much prefer that the output of that command looked like this:  bash happy   Is there a way to tell grep to only output the items that match the grouping (or a specific grouping) in a regular expression? Alternating sum of squares of binomial coefficients How to move a database from SQL Server 2012 to SQL Server 2005 What are my options if I need to move a database from SQL Server 2012(32bit) to SQL Server 2005(64bit)?  I know I cannot:   restore a backup of the database on SQL Server 2005 detach &amp; attach   I know I can:   use import data wizard, and I tried it on one database, but it only moves data, and even that was troublesome as I needed to do a lot of work creating temp tables to maintain identity columns, recreating all FKs, indexes etc.    Is there an easier option? How do open files behave on linux systems? Is there an GUI Designer for python? Is there a GUI IDE for programming python just like java has netbeans?  I wanted one where we could drag &amp; drop test boxes &amp; labels just as we do in swing components using netbeans or eclipse.  Or is there an add-on present in either netbeans or eclipse itself? You can reach this IP address  (if my computer is online). I want to assign a domain to it so I wonder how is that possible when I have no DNS? I do own my domain which is ".com". My IP is static.  Thanks We are planning a trip with a bike rack attached to our trailer hitch. What is the best way to lock the bikes while the vehicle is unattended? I see some racks have locks on the knobs but they don't seem very strong.   What do you suggest? Had it not been vs If it were not for I've just seen the following sentence on a band's biography:     Had it not been for a studio theft, the band might never have made that song.   Then I was wondering if I can change this sentence to:     If it were not for a studio theft, the band might never have made that song.   Is the second sentence correct? Are they interchangeable?   Thanks in advance. How does the loopback interface work How do I disable "Workspace dock" (a bottom panel with the list of open windows and a workspace indicator-cum-switcher), the one that is over "Plank" in the screenshot below?    I'm using Ubuntu 17.10. Is there a way to enable/disable a wireless network interface via the command line (so I can put it in a bat file)?  When I'm in the office I use a wired connection, but Windows still occasionally bugs me about my wireless connection not being connected (even though I turned off the option for notifying me when there's no connectivity).  I'm guessing the only way to stop it from bugging me is to disable the interface, but I'd rather not have to go into the network settings every time I need to do so.  I'd like to set up a bat file or a shortcut that I can use to enable/disable the wireless (preferably a single one that toggles the current state), and then just set up a keyboard shortcut for that.  I just have no idea how to do so from the command line. Duplication formula for gamma function Using the  for $\Gamma(x)$ and $\Gamma\Big(x + \frac12\Big)$, how can I prove the ? This is problem $10.7.3$ in the book , by Boros and Moll.  Any help is highly appreciated. How to set up beamer to grey out past items but hide future items? Where To start Learning With Salesforce Development