I am just wondering if there is a list of the related Mathematica functions that correspond to Octave functions.
For example.
ones(n) maps to Array[1 &, n]
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I closed this question because rm -rf convinced me that what this answer was intended to do is ultimately impossible: that there is simply no way to give an approximate one-to-one mapping of functions between Octave/Matlab and Mathematica; apart from a few limited cases any recommendations are going to be localized and opinionated rather than truly informative.
This answer may remain for the time being but it should be considered deprecated.
As far as I know there isn't one, so let's make one together. This is a Community Wiki post.
The idea is for one person to give an Octave/Matlab function of interest and describe what it does, then other users can recommend substitutes. The community can improve and curate those recommendations. An example entry:
ones
ones(n) builds an n-by-n array of ones
Array[1 &, {n,n}]ConstantArray[1, {n,n}]
ones(n,1) builds an array of zeros of length n
As an alternative to the above
Range[n]^0
This is about as fast as ConstantArray and it's shorter. :-)
zeros
zeros(n,1) builds an array of zeros of length n
Array[0 &, n]ConstantArray[0, n]Range[n] * 0
Also see ones above.
eye
eye(n) builds the identity matrix of dimension n
IdentityMatrix[n]
for
for i=1:n ... end
Do[..., {i, 1, n}]
Use Table instead of Do to collect results into a list. See also Array (and Function).
IMAGE PROCESSING
Basic Import and Export
imread('image.png') Read image from graphics file
Import["image.png"]
imwrite(img,'image.png') Write image to graphics file
Export["image.png","png"]
Image Type Conversion
rgb2gray(img) Convert RGB image or colormap to grayscale
ColorConvert[img, "Grayscale"]
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$\begingroup$ The 3rd alternative for
onesis a bit like this function for obtaining $2^n$:powerof2[n_] := Length@ReplaceRepeated[{0}, (0 -> Sequence[0, 0]), MaxIterations -> n] // Quiet$\endgroup$– aclCommented Jul 22, 2014 at 16:10 -
1$\begingroup$ @Mr.Wizard Oh, I just found this on Wikipedia: "In fact, Octave treats incompatibility with MATLAB as a bug [...]". I think we are safe :) $\endgroup$– sebhoferCommented Jul 22, 2014 at 16:55
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2$\begingroup$ @Mr.Wizard Well, if we want to list all ways to replace MATLAB's
for, it's going to take a while and will includeOuter,Inner,Map,Apply,Cases,Select, and many more functions. That's exactly why I don't think it's a good idea to learn Mathematica based on such a list. $\endgroup$– SzabolcsCommented Jul 22, 2014 at 17:07 -
2$\begingroup$ @Szabolcs I hope no one thinks this is the right way to learn Mathematica. Rather I hope it becomes a useful reference for those making the transition. I'm sure there are many possibilities for getting lost down the rabbit hole but that's what curation is for. $\endgroup$ Commented Jul 22, 2014 at 17:10
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ones(n)probably would beConstantArray[1, n]. However, that creates a list (or vector) ofIntegerentries, which means that if you try to do any arithmetic with it it will be done with exact numbers. This is much slower than with reals. This sort of booby traps are everywhere in mma. $\endgroup$res = sort(a)does the same asres = Sort[a], but[~, ind] = sort(a)isind = Ordering[a]despite the function being calledsort. And then[res, ind] = sort(a)is{res, ind} = Through[{Sort, Ordering}[a]]or{res, ind} = {a[[#]], #} &@Ordering@a, both of which would be too advanced for someone making the transition from MATLAB to Mathematica. $\endgroup$