# torekp

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1. ## Initialize 2D array

I do this kind of thing fairly often, so here are the VIs I've created for the purpose. I'm sitting at a Labview-less computer right now, so I can't check to see if these call any of my other VIs, but I don't think they do. Labview 8.5.1
2. ## logistic regression in LabView

QUOTE (Anders Björk @ Jul 2 2008, 03:15 PM) Thanks for the ideas. Without buying the Toolkit from NI (advanced signal processing, I think it was), how would you set up PCA analysis in Labview?
3. ## logistic regression in LabView

How would you do logistic regression in Labview? Some key points (see the wiki link for more detail), where f(z) is a probability function for some event: The variable z is usually defined as where β0 is called the "intercept" and β1, β2, β3, and so on, are called the "regression coefficients" of x1, x2, x3 respectively. To find the parameters βi, one optimizes them such as to obtain the maximum likelihood of getting the actual observed data. Making a few semi-reasonable assumptions, this amounts to maximizing where L(theta) = the likelihood of getting the observed data, and L* is just the log of that. Why use this approach? In my application, I've got a few categories of scrap metal that I'm trying to sort, let's say Al, Mg, and Zn. They're on a belt, and several diagnostic tests are done as they whiz by; each test outputs one or more real numbers. No one test is absolutely decisive, thus the need for optimizing their weightings. I'm thinking of negating L*(theta) and using Conjugate Gradient nD.vi from the optimization palette. Does anyone have experience with this type of problem, and want to offer advice? If you thinking I'm barking up the wrong statistical/optimization tree, I'd like to hear your thoughts on that too.
4. ## Boxcar (running) average for 1D array

Excellent, bazookazuz. I personally prefer to use exponentially weighted moving averages for most applications. The formula for it is EWMA(i+1) = EWMA(i)*(1-lambda) + latestDataPt*lambda. It's even simpler to compute, and does a nice job of smoothing. The only problem case I've ever seen where you wouldn't want EWMA is where machine error occasionally gives you wild numbers in the (usually negative, for some reason) billions while your real data is order ~ 1. In that case, boxcar moving average is better, because it comes back to sanity faster.
5. ## Custom drawing over a waveform chart

What I usually do is just add two more plots to the graph, set their plot names to "Min P" and "Max P", and use distinctive line-and-point-style combinations. For example, use lines without points for the min and max, and a line with points (or just points) for the latest reading from the sensor. There may be a smarter way. But I don't know it.
6. ## Seeking examples of using relative paths

QUOTE(TG @ Nov 6 2007, 07:32 PM) Here's my main tricks along those lines - I hope this helps. Create a folder "tests" within your user.lib and unzip the contents of the zip into there, thereby creating a sub-folder within tests which holds the VIs and project. The VI "1D_dbl_data_changes" is just a random VI that I'm calling dynamically. A built executable is included. LV 8.2 http://lavag.org/old_files/monthly_11_2007/post-4616-1194402653.png' target="_blank">
7. ## Re-entrant VI: beyond the wiki basics

OK, so I read the Labview wiki on re-entrant VIs. And it gives a few useful examples of when to use or avoid re-entrancy. But what about everyday workhorse VIs? For example, MultiColumnSort.vi (thanks again, JFM). I use this pretty often, occasionally with large data sets, and I could easily see where two of my threads might be trying to use it simultaneously. Should I make it re-entrant just in case? And similarly for all potentially large number-crunching operations? What about database communication VIs? Say I've got a mid-level VI that opens a connection to an Oracle database, reads a table, and closes the connection, and I use this mid-level VI all over the place. Make it re-entrant? In general: any good rules of thumb, not already contained in the aforementioned wiki, would be appreciated.
8. ## writing text file

QUOTE(takimidante @ Sep 28 2007, 09:37 PM) I'm not sure I understood your question, but is this what you want? It allows the user to view or modify the string array (Table) before saving it to the file. One thing to watch out for, I put the date and time on a separate line of the file instead of being on the first line like you had it. I like my way better, of course, but you might want to change it back.
9. ## SCC, subVIs, and multiple calling VIs

QUOTE(Ben @ Oct 1 2007, 03:42 PM) Brilliant. I'm doing it. There aren't that many Labview projects in my whole workplace so it won't be too hard to retrofit. The Quick Check could also examine a list of recently changed subVIs and tell you which top level VIs depended on them.
10. ## SCC, subVIs, and multiple calling VIs

Sometimes you just haven't left yourself enough extra connectors on the connector pane and you need to change your subVI's connector pattern. Or you find a strange behavior in a subVI (how it handles negative numbers, maybe) and you want to change it but can't remember how your other projects used this subVI. Maybe they needed negative numbers to be handled in that strange way. However we get there, I think most of us have had the experience of changing a subVI for the sake of one caller, only to break another calling VI in a different project. I know I have. Can any Source Code Control provide a security check against this? That is, can it notify me when I try to check my subVI back in, "this may affect ProjectX.vi and ProjectY.vi", or some such? I haven't selected an SCC provider yet, but I was looking at Microsoft Visual Source Safe and didn't see it.
11. ## keeping multiple backups of a file

QUOTE(yen) Pretty much what I'm doing, except I timestamp the filenames not folders, and I do keep selected files older than N. QUOTE(NormKirchner @ Aug 29 2007, 01:42 AM) Am I stating the obvious, but what about source code control? It does go the 'everyting' route, but I know for sure that Perforce optimizes the different versions so it does not necessarily save the entire file for each version. Not obvious at all (or maybe I'm just slow). But this means I'd have to start using source code control - probably a desperately needed idea even without this side-benefit... Thanks for the suggestion.
12. ## keeping multiple backups of a file

Say you've got some file that you keep changing over and over. You want to save some backup copies but there's no need to save every single one for all eternity. Maybe you want to keep everything less than a week old, then keep another from a month or so ago, then another from 6 months, then another from a year or so ago - for instance. Or maybe something else. What other ways of managing the backlog of backups make good sense? (Besides the obvious methods, keep everything, or keep nothing.) Here's what I wrote that does what I just described, for what it's worth. I already want to add one feature to it, which is to keep at least N backup files, no matter what. Where N is the number of "ages" to keep (3 in the above example). LV 8.0. http://forums.lavag.org/index.php?act=attach&type=post&id=6777http://forums.lavag.org/index.php?act=attach&type=post&id=6778
13. ## Deviations of the mean

QUOTE(tcplomp @ Aug 21 2007, 04:33 AM) May I suggest another extremely useful moving average, the exponentially weighted moving average: http://en.wikipedia.org/wiki/Exponential_smoothing''>http://en.wikipedia.org/wiki/Exponential_smoothing' target="_blank">http://en.wikipedia.org/wiki/Exponential_smoothing Easy on the processor and on the memory.
14. ## Is the day of the "Queued State machine" behind us?

QUOTE(shoneill @ Aug 15 2007, 07:42 AM) Can you explain this in more detail to someone like me? Someone who's "Not A Real Programmer, But I Play One At Work."
15. ## Dynamic Array Size

QUOTE(abuch06 @ Jul 27 2007, 03:07 PM) I'd like to suggest two alternate ideas instead of your 3D array: (A) a 1D array of clusters, each cluster containing {channel, value, time} (B) a second 2D array containing zeros or NaNs (Not A Number's) wherever value < 2, elsewhere the original values. Idea (B) lends itself to display on an Intensity Graph: http://forums.lavag.org/index.php?act=attach&type=post&id=6504http://forums.lavag.org/index.php?act=attach&type=post&id=6505
16. ## traveling sensor optimization problem

QUOTE(Kevin P @ Jul 18 2007, 01:41 PM) 1. Right, the X-Y boundaries are pretty well defined. 2. The speed ratio of belt and sensor is known, and max sensor speed >> belt speed. 3. The sensor produces a small XY image array, where "resolution" improves as you allow the sensor more time to collect. 4. Objects are as time-consuming to inspect as I want them to be, so to speak. It's probably more important to get large-area objects well-inspected than small-area ones, but I haven't gotten far enough to worry about that yet. It probably is preferable, to a modest degree, to inspect from a position near the centroid of an object - or rather, not too close to the edge. I've decided that delta-X proximity from the sensors most recent position is not too important. The sensor is fast enough to get where it needs to go, as long as it can settle there for a little while after arriving.
17. ## Windows 2000 Server

Here's a fun fact: if you use LV 8.0 to create an executable and an installer for it, you can install it on a Windows 2000 Server machine, no problem: not even a warning. Even though, according to NI phone support engineers, you're not supposed to do that. I found only one significant problem on the 2000 Server: some file writes were very slow, compared to the speed on WinXP. Otherwise, my apps worked fine. If you use 8.2.1 to create the installer, you cannot install it on a Windows 2000 Server machine. You are informed that the machine does not meet the requirements. There is no choice, no "Warning: this computer does not meet the requirements; some or all functionality of the program may fail; install anyway?" I'd rather get a warning, and let me try it at my own risk. Oh well, now I have installed 8.0 onto my WinXP, so that I can "save for previous" and then create executables from 8.0 for distribution to the Server machines.
18. ## traveling sensor optimization problem

I'm designing an algorithm to tackle my problem, but I have the feeling I'm re-inventing the wheel. Not only that, but my wheel feels kinda square, and I'm hoping there's a round one out there, that you know about. I've got a moving belt with parts randomly scattered on it. The parts are NOT singulated: if you draw a line across the belt, chances are that you'll find one or two parts there, and occasionally more. Some parts are bigger than others. There is a camera near the feed end of the belt, which identifies the locations of the parts. Further down, a traveling sensor (which travels only across the width of the belt: call this the X-direction in a Cartesian coordinate system) visits the parts for a more detailed inspection. The sensor travels fast enough that there is not much worry about going from one side of the belt to the other. I thought that would be a problem, and asked for advice on it in the past, but it's not a big issue, as long as the sensor is allowed to have some settling time after each jump. However, the sensor can only visit one part at a time. It must divvy up its visiting-time between the various parts that occupy the same line. I want to optimize the accuracy of the analyses that the sensor gives, and the accuracy is proportional to something like the square root of the amount of time spent on each part. Therefore - I think, correct me if I'm wrong - I want to make the time spent on each part as nearly "fair" (equal) as possible, while of course spending "more than fair" time on a particle if it's the only one around. I don't want the calculation to take much processor time. I've got an idea how to do it, but let me not bias your thinking yet. Bear in mind that it's possible to encounter clumps of parts, perhaps five or more side by side. It's also possible, and common, for a densely populated area of the belt to go on for some length, so that perhaps 50 parts or so go by before the sensor gets a "breather" (brief empty stretch of belt). The camera takes data in "frames", which are approximately square areas of belt, and the sensor path calculation is independent for each frame. If a part straddles two frames, the Vision software will pretend that only the larger half exists, so I never need to worry about any stretch of belt longer than a single frame. The camera and Vision software make it natural to mentally divide the belt into a number of thin lines. Approximately one line goes by per millisecond, and we can think of the sensor as being able to occupy any X-location during each millisecond, although it would not be wise to jump around too much from part to part. Each part should be dwelled upon for a while, then go to the next.
19. ## Threshold 1D Array search

QUOTE(Gary Rubin @ Jul 13 2007, 01:24 PM) Beautiful, thanks. Just what I wanted. :thumbup: This goes straight into my re-use code folder.
20. ## Threshold 1D Array search

QUOTE(Gary Rubin @ Apr 4 2006, 02:18 AM) Gary, could you please post this binary search VI?
21. ## Saving VI settings to a file

Thanks for all the great ideas guys. I wonder, is there any way to make the files not only human-readable but also very user-friendly, for example by putting HTML tags/bookmarks into it so the reader can jump to the parts he considers interesting? Some of my programs have a very large number of settings.
22. ## CR Editing of Content

When I edit my description after noticing a typo, do I have to re-submit my Zip file even though it hasn't changed? I did so, just to be safe. I noticed that there is a check-mark for "delete old screenshot?" so I just unchecked that and didn't submit a (repeated) screenshot, but I wasn't sure about the Zip file.
23. ## classy datalogs, upgrading, and error 1401

NI confirms: this is a bug, but they say that it will not happen on the next upgrade. They wrote to me: QUOTE I gave up on my old files; they weren't all that vital. Like you, I wasn't far from the beginning of my project.
24. ## self-decimating array for storage

Hey ragglefrock, it was worth it, you taught me an important lesson. Namely, if performance really counts, and a VI will be called many times, make it a subroutine. Good to remember.
25. ## self-decimating array for storage

QUOTE(ragglefrock @ Feb 13 2007, 04:59 AM) After making a better version of my idea for the Code Repository, I tried out your suggestion, and found that the native Quotient & Remainder function is faster. Attached, my slightly modified version of your VI, plus the test VI.
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