I am working on a data set that has 930 rows and 5 columns. I'm implementing KNN Regression with bootstrapping and my RMSE is almost 400 (depending on different cross validated outputs). I read  and one of the answers mentioned that if the training and test RMSE are similar, then the model is good; any my training error is close to 400 too. I've tried searching online for reliable sources to know if this high an error rate is acceptable, but I've mainly read articles and posts that say the closer the RMSE is to 0, the better, which definitely is not the case here.   Any advice is appreciated!
I've fitted my model and am trying to understand whether it's any good. I've calculated the recommended metrics to assess it ($R^2$/ AUC / accuracy / prediction error / etc) but do not know how to interpret them. In short, how do I tell if my model is any good based on the metric? Is an $R^2$ of 0.6 (for example) sufficient to let me proceed to draw inferences or base scientific/business decisions?     This question is intentionally broad, to cover a wide variety of situations that members frequently encounter; such questions could be closed as duplicates of this one. Edits to broaden the scope beyond the metrics mentioned here are welcome, as are additional answers - particularly those that offer insight about other classes of metrics.
I read that     A typical stream cipher encrypts plaintext one byte at a time, although a stream cipher may be designed to operate on one bit at a time or on units larger than a byte at a time.   (Source: , William Stallings.)  A block cipher encrypts one block at a time. The block may be of size one byte or more or less. That means we can also encrypt a block of one byte by help of a stream cipher as a stream.  So, what exactly is the difference between a stream cipher and a block cipher? The number of solutions to an $n^{th}$ order differential equation. For an $n$th order differential equation, why are there always $n$ solutions? Why exactly $n$, not $n - 1, n+1$ or infinite many?    Addendum by LePressentiment :   This is motivated by P176 on Strang's Intro to Lin Alg, 4th Ed. An $n$th order differential equation, how many basis functions does it have? I'd guess $n$, because the diffl eqn have $n$ linearly independent solutions (predicated on Julián Aguirre's answer), all of which look to span the nullspace/solution space of the homogeneous ODE. Humans don't digest fibre, and nor do any animals, but some creatures have micro-organisms (bacteria, I'm guessing) in their gut which digest fibre for them.  My question is, could humans take some sort of pill and establish our own fibre-digesting colonies in our intestines?  Has this been tried?  Supposing it could be done, would you suppose it would have any negative effects on our health?  (i.e.. would those whose gut digested fibre for them be stuck on a low-fibre diet?).    Purpose of question: just wondering.  It would be cool to be able to eat bark. Will I be demoted to a lower league in Starcraft 2 if I don't play? I've just been promoted from platinum league to diamond and master pretty fast (in 4 vs 4). This was totally amazing for me but I'm afraid I will be demoted again to a lower league as fast as I came higher.   If I don't play any 4 vs 4 anymore, will they demote me to a lower league automatically or do they only do so, if I play? Diagonalizable Operators and characteristic polynomials Let $A$ be an $n\times n$ diagonal matrix with characteristic polynomial $(x-c_1)^{d_1}\cdots(x-c_k)^{d_k}$, where $c_1,\ldots,c_k$ are distinct. Let $V$ be the space of $n\times n$ matrices $B$ such that $AB=BA$. Prove that the dimension of $V$ is $d_1^2+\cdots+d_k^2$. Given six numbers $x,y,z,a,b,c$ which satisfy the following relations. Express $x+y+z$ in terms of $a,b,c$ Given six numbers $x,y,z,a,b,c$ which satisfy the following relations $y^2+yz+z^2=a^2$ $z^2+zx+x^2=b^2$ $x^2+xy+y^2=c^2$ Express $x+y+z$ in terms of $a,b,c$    My attempt: $\dfrac{(y^3-z^3)}{(y-z)}=a^2,\dfrac{(z^3-x^3)}{(z-x)}=b^2,\dfrac{(x^3-y^3)}{(x-y)}=c^2$ But this step didn't seem to help. So I tried adding and expressing $k(a+b+c)^2$ but some other unmanagable elements came along. I could not think of any other way to approach the problem. Please help. The word "quad" generally means 4. Quadratics don't have 4 of anything. Can anyone explain where the name comes from? Why are all snaps being mounted and listed as block devices or partitions for Ubuntu 18.04? As of Ubuntu 18.04 running lsblk shows 16 snap loops (2-3 times for each snap). The question is, why are they being listed as results for lsblk, fdisf-l, and blkid?    It creates a lot of clutter from the actual disks drive partitions I need to see, namely /dev/ partitions. I know a purported duplicate of this question exists, but it only asks why three loops are being listed per snap. I want to know why these snaps are being listed in the first place, and the purported duplicate does not answer this (perhaps those marking this as duplicate could help me by explaining why it is a duplicate). Technically, they qualify as file systems (which I neither created nor asked for), but they are getting in the way of the information output for the /dev/ partitions I am interested in. This becomes a problem when fdisk -l outputs a three page+ list filled mainly with snaps.  The output of a recent (1 week old) Ubuntu install and I have not installed any snaps:    $ lsblk   NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT   loop0    7:0    0  14.5M  1 loop /snap/gnome-logs/37   loop1    7:1    0   2.3M  1 loop /snap/gnome-calculator/170   loop2    7:2    0  86.6M  1 loop /snap/core/4486   loop3    7:3    0  86.6M  1 loop /snap/core/4650   loop4    7:4    0   1.6M  1 loop /snap/gnome-calculator/154   loop5    7:5    0  14.5M  1 loop /snap/gnome-logs/34   loop6    7:6    0   3.3M  1 loop /snap/gnome-system-monitor/36   loop7    7:7    0   2.3M  1 loop /snap/gnome-calculator/178   loop8    7:8    0    13M  1 loop /snap/gnome-characters/101   loop9    7:9    0   3.7M  1 loop /snap/gnome-system-monitor/45   loop10   7:10   0 139.5M  1 loop /snap/gnome-3-26-1604/64   loop11   7:11   0   140M  1 loop /snap/gnome-3-26-1604/59    loop12   7:12   0   3.7M  1 loop /snap/gnome-system-monitor/41   loop13   7:13   0    21M  1 loop /snap/gnome-logs/25   loop14   7:14   0  12.2M  1 loop /snap/gnome-characters/69   loop15   7:15   0    13M  1 loop /snap/gnome-characters/96   sda      8:0    0 298.1G  0 disk   ├─sda1   8:1    0   512M  0 part /boot/efi   └─sda2   8:2    0 297.6G  0 part /   sr0     11:0    1  1024M  0 rom     (supplemental screen capture of above text):     My snap list shows 6 results:       core   gnome-3-26-1604   gnome-calculator   gnome-characters   gnome-logs   gnome-system-monitor     Meanwhile, gnome-disk-utility shows nothing at all for snaps, only showing my HDD and optical drive.    It won't be very efficient if every installed snap gets listed as a block device (2-3 times each to add). Should I expect future updates to deal with this?  Edit: fdisk-l also dumps out a very long list with 16 instances of these "disk loops" (Disk /dev/loop0, Disk /dev/loop1, etc., each with details which I won't show here because it's too long). This can't be intended behaviour, can it? blkid also lists 16 loops, as TYPE="squashfs". At least parted -l works as expected, only outing my actual disk partitions.    I just tested this, and installing more snaps does add more to the lsblk output. Therefore, fdisk, lsblk, blkid could have potentially huge output lists, according to the number of snaps available, and installed. What are the limits of house-elf apparition? I know Wizards can't apparate where they want on the Earth, except if they are very powerful but what about a house-elf ? Their magic is different so I was wondering if they can apparate wherever they want or if they have a limit too. What happens when identical overlapping effects have their end-condition met? Trying to identify a very old short story about aliens colonizing human bodies Don't remember the exact start to the story, but it went something like "walking along a path" or something, and when he hears what sounds like a shotgun blast behind him, he then feels something strike him in the butt. He passes out, and when he awakens, he discovers that the "shotgun blast" was actually a miniature spaceship that exploded and shot miniature aliens into his body. The aliens prove to be very beneficial because they clean up all the toxins and other poisons in his body. They can be transmitted through kissing or sexual activity.  Any help with the name of the story would be greatly appreciated.  Dan Collapsing a stream of multiple lines into one line I have a file containing a a large number of lines, each of which contains a bunch of numbers which are separated by spaces. I process this data in a pipe in some way, and then I want to collapse the multiple lines into a single line of all the numbers separated by spaces.  Is there a standard command-line utility I can use to do this? It seems like most line-by-line utilities won't mess with the newlines... Is there a fast way (without looping over all edges/faces/verts) using ops.mesh or bmesh to get the lists of indices associated with mesh islands as shown below? These islands are part of one mesh but are disjoint from each other.    I know how to select the boundaries by running the operator Select boundary Loop or calling bpy.ops.mesh.region_to_loop() but can't find any API calls to return the vert/edge/face indices associated with the individual islands. I found this one on UserVoice, and I thought it was fitting to bring it up here for further discussion.  "Stack&nbsp;Overflow already works with Mobile Safari, but the experience is far from optimum. I believe an iPhone-optimized version (or maybe even a native client) would be perfect. I can help with either."  I personally think a some kind of mobile version of Stack&nbsp;Overflow would be great for using as a reference, but using it to ask questions would probably get cumbersome if you had to type up a long question with full description. However, using it to look up an answer when you're away from your desk would be awesome.  But, why not just use the regular Stack&nbsp;Overflow? Well, we all know that the small, touch screens get cumbersome to use when navigating websites built for desktops. Why do the directories /home, /usr, /var, etc. all have the same inode number (2)? Why did Palpatine wait so long before giving Order 66? Get Response header when 401 occurred Sometimes it is convenient to use an absolute path to include a preamble. To do so, I use the following "hack":  \documentclass[a4paper, 12pt]{article} \newcommand{\folder}{/path/to/folder} \input{\folder/preamble}  \begin{document} \end{document}   Now my question is, whether there is a more elegant way to do this, especially a way which is compatible with one of the flatten scripts from  ? Show that $n$ lines separate the plane into $\frac{n^2+n+2}{2}$ regions Show that $n$ lines separate the plane into  $\frac{n^2+n+2}{2}$ regions if no two of these lines are parallel and no three pass through a common point.   I know we start with the base case, where, if we call the above equation P(n), P(0), for 0 lines would be 0.  But I really have no idea how to begin the inductive step.  How do we know what k+1 we're supposed to arrive at?  Thanks! Sync +- 70 000 records from CSV into drupal I have a CSV file with approx. 70.000 records that I want to import into Drupal 7. Once this is done the client will provide a new CSV file on a daily base that has to sync the updated rows to Drupal.   I wrote a import with  and the  module, but in both cases it takes like forever to import the 70.000 rows. Is there any other solution to import the data faster in Drupal 7?