Ask MetaFilter questions tagged with matlab

How do you open .MAT files with variables?

cali59 — Thu, 10 Dec 2009 13:13:09 -0800

I need help opening Matlab workspaces I'm on a computer running Windows XP. Until today, Matlab workspaces (.MAT) opened just fine, but then out of nowhere it reverted back to thinking they were some sort of file associated with Microsoft Access. I went into Windows Explorer > Tools > Folder Options > MAT > Advanced > Edit and changed it back to opening with the Matlab.exe file, but now the workspace variables don't appear. Googling hasn't helped much.

Does anybody know what the nuance is to opening these files with the workspace variables? Perhaps if someone could just copy the settings they have to here that would be enough. Thanks.

How do you get the mat file name?

cali59 — Tue, 15 Sep 2009 03:50:49 -0800

How do you get a Matlab script to know the name of its own .mat file? I have a bunch of .mat files that have descriptive names (ex "round fluffy A.mat", "square fluffy B.mat") and I'd like to process the data and generate a figure with the name of the mat file, only .fig. I don't want to have to hard code the filename, or use a dialog box to input it or anything, I just want a way to be able to retrieve the argument that was used in the command that shows up when you double click the .mat file, namely

load('C:\PATH\FILENAME.mat')

I'm sure there's plenty of other ways I could be doing this, but after searching google and MATLAB help, it's kind of driving me nuts that I can't just find a simple way to do this. Am I overlooking something? Thanks.

How much should a contract programmer cost?

LadyOscar — Thu, 27 Aug 2009 11:20:48 -0800

How much should we pay a contract programmer to migrate some code for us? Is it customary for the programmer to present a bid, or do we come up with an amount to offer? Our biology lab is looking to migrate some complicated MRI data analysis from a Linux box to a Mac. Currently we're using a mixed bag of Perl scripts and Matlab modules set up by someone who is no longer with the lab. We'd like to hire a programmer to initially just get the whole thing working on the Mac, then later re-write it, probably in Python, to be more streamlined. However, we've never hired a programmer before, and I have absolutely no idea how much they expect to be paid. Per week, what kind of amount are we looking at? (We're in the Los Angeles area, if that makes a difference.)

Also, is this person likely to have a price that they'll quote us, or do we have to come up with a number? Who sets the time estimate, us, or them?

Thank you for your wisdom, o business-savvy people!

What's the optimal amount to spend on this raffle?

boghead — Fri, 24 Jul 2009 09:04:13 -0800

There's a monthly raffle at work for 5 parking spaces out back. There are about 30 people in my office. There's no limit to the amount of tickets you can buy. You can only win once. Otherwise, parking costs about $4 a day, or about $80 a month. Raffle proceeds go to charity. What's the optimal amount to spend on this? I should tell you also that this question is purely academic because the raffle has been discontinued. But I still want to know what you all think because work is boring as all get out.

What's the best way to figure this out? One friend said she'd use a stats program, another said Matlab. I was thinking maybe a nice line graph with asymptotes and bright colors and such?

I figure the absolute most you would want to spend on this raffle would be $80, only because it goes to charity. Also, I'm assuming no one else in the office ever bought more than 2 or 3 tickets.

How can I get a smooth nice math font in LaTeX?

molecicco — Mon, 06 Apr 2009 03:24:06 -0800

Why are LaTeX math fonts so terrible? Or am I missing something? I want to get some nice titles on a legend for a Matlab figure, and I have to use the LaTeX interpreter for some accents, but when I import the figure into Word the resulting font is very pixelated and just plain garbage. How do I get smooth and clear math fonts out of LaTeX? I am bound to using the LaTeX interpreter and $$ delimiters in order to get a dot above a Q, ie: $\dot{Q}$. But the default, italicized font is blurry and pixelated. Even when I use, say $\mathrm{\dot{Q}}$ its still pixelated. And \mathtt gets rid of the dot.

I'm printing the figure to BMP and inserting into the Word document... I have to use Word even though I'd rather be using LaTeX. Any suggestions are appreciated!

crop matlab plots

pravit — Thu, 06 Nov 2008 17:18:10 -0800

How can I automatically crop the whitespace in Matlab plots pasted into Word? I find a not insignificant portion of my time in report writing is spent cropping the extra whitespace around Matlab plots that are pasted into Word. Is there some way to eliminate the whitespace automatically, either with some nifty Word trick or by forcing Matlab to generate windows without so much whitespace around the plot? Thanks.

Representing a tree in Matlab?

fake — Mon, 06 Oct 2008 21:16:18 -0800

What is a good way to represent an N-ary tree in Matlab? I am working on a classic AI problem. (Minimax with Alpha-Beta pruning). I need to represent all possible game states in a tree. How would you go about expanding the tree and representing it in some data structure?

Bimodal or am I biased?

halogen — Tue, 23 Sep 2008 19:53:08 -0800

StatisticsFilter: how can I find out whether my data is bimodal? I have no statistics skills whatsoever, and I would love to have this figured out before I return to campus tomorrow morning. Please help!

Background: I have several sets of 70 numbers each (they represent the lengths of bacterial cells infected with different phages). I want to show that there is a significant difference between the two sets. While my averages look very good, adding error bars negates my findings. For example:
Set 1: Average 6.83, Standard deviation 1.67.
Set 2: Average 4.1, Standard deviation 1.00.

Possible explanation: Let's look at one set at a time. There is a chance that I infected my bacteria with less phages than I planned to, so that not all the bacteria were affected--which would effectively split the populations sampled in each set into "infected" and "uninfected", and presumably they would have different length distributions. Can I test for this before I repeat my experiment (I plan to do that anyway, but still want to know if my findings are significant at this point)?

Googling taught me that Hartigan's Dip Test is what I need. A stranger kindly posted Matlab functions for the test.

Problem: I have Matlab installed on my computer, but I have never used it and I have no idea what to do at this point. I have a column of values in Excel, and even if I manage to enter it as a set in Matlab (although my attempts so far don't look good), I don't know how to run the test. If you can show me how to run it, how would I interpret the results so that they would be meaningful to me (provided I get Matlab to print them)? Please, please, can you help me with that?

Do you have any other suggestions for what to do to my data (remove outliers? how?) or how to look at it in order to see what's going on? (I can post the dataset somewhere if necessary.) Thanks!

Difference between two correlated normally distributed random variables

PercussivePaul — Sun, 14 Sep 2008 21:35:30 -0800

A statistics question about dependent normal random variables. My stats is really rusty so forgive me if I say something that doesn't make sense.

I have two random variables, X1 and X2. Both are normally distributed; let's say mean1=7000, mean2=7500, and the standard deviations are both 15. I am interested in knowing the probability that X1 < X2.

The trick is that these variables are not independent. They should be strongly correlated. That is, if X1 is really big, then X2 should also be pretty big. I don't know the exact correlation; maybe it's between 0.7 and 1.0. I plan to make a bunch of graphs leaving that as a variable. So let's assume for now that it's 0.8.

If they were independant I would know what to do, but I can't figure out to handle the correlation. I've been mucking around in Matlab but all I can figure out how to do is make a multivariate normal distribution with all the parameters above; I don't know how to go from there to figuring out if X1 < X2. Help?

How do define points as spheres in MATLAB

kaozity — Tue, 30 Oct 2007 14:00:53 -0800

In MATLAB, how do you represent moving objects not as points in 3d space but as spheres with a certain radius? I am working in MATLAB to model spheres that need to touch each other in a continuous space. At the moment they are defined by x, y, and z coordinates and a certain vector velocity and are represented by points. I want them to be a 3d shape so that their surfaces can meet. I have been attempting to do this by setting the "markersize," however I cannot seem to figure out the algorithm that MATLAB uses to relate the arbitrary number for markersize and it's actual radius as compared to it's axes. Does anyone have suggestions for how to use Markersize and know it's actual radius or another method of representing a point as a sphere? Is my only option to define my own sphere at that point?

How should my program collect MIDI messages?

springload — Sat, 13 Oct 2007 18:11:31 -0800

Where can I find enough info on Windows' MIDI API to start using it? I have a Behringer controller with a "USB MIDI" interface (a USB cable goes straight from the box to the computer). I want to catch the messages sent from this unit in a Matlab program. There should be built-in support for this in Windows, but I don't find much documentation about it. Can someone please explain to me what DLL or ActiveX element to load, how to create a session, what functions to call and all the other details needed to see some MIDI messages on the screen?

laptop for matlab and photoshop

garethspor — Mon, 18 Jun 2007 17:53:53 -0800

stolen laptop/replacing said computer question: My old 17" Macbook G4 was stolen this moring :( I need a good laptop for running matlab. open to macs or PCs... So pretty much I used this computer for running matlab and photoshop primarily. I'm fairly confident that my renters insurance will cover it and I will be able to replace it. What I'm wondering is what computer to get if I'm really only concerned with running these two programs. I would be all about getting another mac but matlab was such a pain to install on OS X and seems impossible to install on the newer intel macs. Have I been misled? Can we now run matlab on intel macs? Or should I find a good PC laptop that can crunch and store lots of numbers and images? Probably looking to spend under $3k on this new one. Any suggestions hive mind?

MATLAB axis relabeling

dmd — Tue, 12 Jun 2007 07:55:53 -0800

Customizing MATLAB axes: Transform unixtime into date labels? MATLAB gurus:

My figure's X axis currently consists of unix timestamps. I would like it to be labeled as YYYY/MM instead, and I'd like MATLAB to continue to work its magic as far as redrawing the axis prettily when the window is resized.

I found this library to convert unixtimes to year/month and this tutorial on customizing axes, but I still need some more help. (I can convert the times just fine, it's the axis stuff I don't understand.)

Help me get up to speed with Matlab.

fake — Wed, 23 May 2007 08:31:29 -0800

What are the best online and offline learning materials for Matlab? I'd love to see some online videos to get me past the interface, pick up a solid book on the topic and dive in. Free would be best, but paying for books or video training does not phase me, especially if the quality is very high.

I'll be using Matlab primarily for modeling and image processing, towards my PhD in Visual Neuroscience, if that helps anything. I've got little to no programming experience, beyond scripting in Alias Maya.

Also, are there online communities for Matlab like there are for 3D modeling packages/compositing/etc?

Make a list of matrices in MatLab

atrazine — Thu, 01 Mar 2007 11:15:36 -0800

How do I implement a Matrix (or list) of matrices in MatLab? I need to make a list of matrices, the matrices are not all the same size. This seems like it should be really easy, but I can't figure out how to do it.

Drawing with Fourier descriptors?

dmd — Sun, 05 Nov 2006 14:55:22 -0800

I need help finding code to draw (not extract) fourier descriptors. I need to draw some simple FD-specified shapes (basically little blobs - power at only a few frequencies). I'm having a lot of trouble doing it myself, and it seems that this isn't something that anyone else ever does - there's lots of code out there for taking an existing contour and fitting it, but I need to go in the other direction. Anyone have some code or know where I can find it? I'm language-agnostic; I'm happy to translate from whatever I get into the language I'm working in.

printing matlab figures to memory

garethspor — Sat, 28 Oct 2006 11:36:42 -0800

MatLabFilter: Printing figures to memory? I know that I can use the versatile print command to print a figure to a file. But how might I be able to turn a figure into a matrix in matlab's memory? previously I've printed figures to files then opened those files into memory but this seems like a horrible kludge. any way to turn an onscreen figure directly into a matrix? specifically I'm interested in creating really busy figures using typical matlab handle graphics, but I'd like to periodically flatten the figure into a matrix then add to it continually without bogging matlab down with a million graphic objects that would take an eternity to render. any ideas?

Pairing data and video frames in MATLAB

freddymungo — Mon, 24 Jul 2006 05:39:59 -0800

I have a 10 FPS video, and a set of numerical data for every frame in the video. How can I pair up each frame with its set of data in MATLAB?

Help me find shareware/freeware to analyze titration data, please!

445supermag — Sun, 02 Jan 2005 09:50:40 -0800

I'm looking for shareware/freeware or Matlab .m files that will do Target Factor Analysis or Evolving Factor Analysis or some other chemometric technique that will allow me to analyze some titration data. The first few spectra are of a pure component and the later spectra are a mixture of components that I don't basis spectra for.

Should I use MATLAB or GAUSS for statistical analysis?

Frank Grimes — Mon, 26 Jan 2004 15:16:36 -0800

Does anyone have experience using MATLAB or GAUSS for statistical analysis (specifically for financial modeling)? Pros/Cons/Prices of one or the other.