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Feb
4
comment Differentiating a Dot Product
You can even write D[xVec.pVec, {pVec}] to get the gradient wrt pVec, or D[xVec.pVec, {pVec, 2}] to get the Hessian. It took me a long time to figure that out...
Jan
26
awarded  Yearling
Jan
25
comment Labelling objects in a picture with numbers
@andy: I'm sorry, but no, I won't give you my email address. I'm not a private tutor. And if I were, I would tell you the same thing: get a good book, read the documentation. It'll be quicker, more fun and you'll learn more that way than by having someone doing your homework.
Jan
24
answered Labelling objects in a picture with numbers
Jan
7
comment Mathematica quine
I'm pretty sure #0 is cheating. It's like fopen("program.c", "r") in C.
Jan
2
comment Specific Mathematica algorithms, for example LU Decomposition
IIRC, on a x86 CPU, floating point numbers on the FPU stack are stored and processed in 80 bit long double format, even when the variable data type is 64 bit double. This can lead to the confusing effect that changing compiler options or reordering (independent) operations can change calculation results, depending on whether a value is moved to a 64-bit memory location or can stay in the stack for the whole calculation. On modern SSE-enabled CPUs, you also have separate commands that work on 64/32bit FP numbers directly. That might explain differences in the last few bits.
Dec
31
comment Why can Format be used on the left side?
I had trouble grasping "definitions" like these, too. Until I stopped thinking about them as "definitions" and started to see them as "replacement rules", i.e. telling the interpreter "if you see something that matches the pattern on the left, replace it with that stuff on the right side of the :=". Then it started making sense.
Dec
16
comment Find the best parallel lines to a given data set
@RahulNarain: Depends on the number of data points. If you have 10^6 or 10^7 points, really simple things might take some time ;-)
Dec
16
revised Find the best parallel lines to a given data set
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Dec
16
comment Find the best parallel lines to a given data set
That happens a lot. Just look up convex hull algorithms and implement one in the language of your choice. Don't try to hand in somebody else's implementation for your own. They'll know. Good luck in college!
Dec
16
comment Find the best parallel lines to a given data set
Do you realize that you posted your question on a Q&A site for the Mathematica programming environment?
Dec
16
revised Find the best parallel lines to a given data set
deleted 280 characters in body
Dec
16
revised Find the best parallel lines to a given data set
added 156 characters in body
Dec
16
answered Find the best parallel lines to a given data set
Nov
25
answered How to ListPlot over an Imported Image
Nov
11
comment Why can I still hear sound when the frequency of the periodic function inside Play is lower than the range of human ear?
@Rojo: Yes, it makes sense to me, too, now. You learn something new every day.
Nov
8
comment Why can I still hear sound when the frequency of the periodic function inside Play is lower than the range of human ear?
@DanielW: I'm curious, what's the connection between speaker size and sound wavelength? For example, I can produce a 50Hz signal with my speakers, although they're much smaller than the 6.9m wavelength.
Nov
6
comment video image recognition
@YvesKlett: On the other hand, when the players get a strong enough electric shock, they should be easier to track ;-)
Nov
6
comment video image recognition
You could try ImageFeatureTrack. But if that doesn't work, prepare to do some serious research. Attaching LEDs to their clothes when they're in the shower might be easier ;-)
Nov
6
comment Running out of memory when partitioning an image with ImagePartition
+1 I usually use a Closing operation instead of a GaussianFilter: It's robust, it removes the characters completely and it doesn't smooth the background brightness (as much). It's slower than GaussianFilter, but with a rectangular mask, processing time shouldn't depend on filter size, either. (Haven't tested that, though.)