wolfram-mathematica - w3toppers.com

Executing code in v.5.2 kernel from within v.7.01 session through MathLink

Here is an implementation based on Simon’s code. It still requires improvement. The one unclear thing to me is how to handle Messages generated in the slave (v.5.2) kernel. Here is my code: Clear[linkEvaluate] SetAttributes[linkEvaluate, HoldRest] linkEvaluate[link_LinkObject, expr_] := Catch[ Module[{out = {}, postScript = {}, packet, outputs = {}}, While[LinkReadyQhttps://stackoverflow.com/questions/4983301/executing-code-in-v-5-2-kernel-from-within-v-7-01-session-through-mathlink, Print[“From the buffer:\t”, LinkReadhttps://stackoverflow.com/questions/4983301/executing-code-in-v-5-2-kernel-from-within-v-7-01-session-through-mathlink]]; … Read more

Import big files/arrays with mathematica

For some reason, the current implementation of Import for the type Table (tabular data) is quite memory – inefficient. Below I’ve made an attempt to remedy this situation somewhat, while still reusing Mathematica’s high-level importing capabilities (through ImportString). For sparse tables, a separate solution is presented, which can lead to very significant memory savings. General … Read more

How do I label different curves in Mathematica?

There’s some nice code that allows you to do this dynamically in an answer to How to annotate multiple datasets in ListPlots. There’s also a LabelPlot command defined in the Technical Note Labeling Curves in Plots Of course, if you don’t have too many images to make, then it’s not hard to manually add the … Read more

Mathematica: Unevaluated vs Defer vs Hold vs HoldForm vs HoldAllComplete vs etc etc

These are pretty tricky constructs, and it’s tough to give clear explanations; they aren’t as straightforward as Lisp macros (or, for that matter, the relationship between Lisp’s QUOTE and EVAL). However, there’s a good, lengthy discussion available in the form of notes from Robby Villegas’s 1999 talk “Unevaluated Expressions” on Wolfram’s website. Defer is omitted … Read more

Mathematica: How to clear the cache for a symbol, i.e. Unset pattern-free DownValues

I’ve made similar functions in the past (but I can’t remember where). Does the following code do all that you need? ClearCache[f_] := DownValues[f] = DeleteCases[DownValues[f], _?(FreeQ[First[#], Pattern] &)] This maybe should be extended to UpValues and SubValues. And the Head of f restricted to Symbol.

Remove White Background from an Image and Make It Transparent

This function implements the reverse blend described by Mark Ransom, for an additional small but visible improvement: reverseBlend[img_Image, alpha_Image, bgcolor_] := With[ {c = ImageData[img], a = ImageData[alpha] + 0.0001, (* this is to minimize ComplexInfinitys and considerably improve performance *) bc = bgcolor}, ImageClip@ Image[Quiet[(c – bc (1 – a))/a, {Power::infy, Infinity::indet}] /. {ComplexInfinity … Read more

Image transformation in OpenCV

Apart from etarion’s suggestion, you could also use the remap function. I wrote a quick script to show how you can do this. As you see coding this is really easy in Python. This is the test image: and this is the result after warping: And here is the code: import cv2 from scipy.interpolate import … Read more

Plot using With versus Plot using Block (Mathematica)

Your question is not so much about Plot as it is about how the scoping constructs work. The main confusion here is due to the differences between lexical and dynamic scoping. And the main culprit is this definition: f[x_] := (vmax x)/(km + x) The problem with it is that it makes f implicitly depend … Read more

The best way to construct a function with memory

Let’s assume our slow function has the signature f[x, y]. Pure In-memory Approach If you are satisfied with an in-memory cache, the simplest thing to do would be to use memoization: Clear@fmem fmem[x_, y_] := fmem[x, y] = f[x, y] This adds a definition to itself every time it is called with a combination of … Read more

How do I find Waldo with Mathematica?

I’ve found Waldo! How I’ve done it First, I’m filtering out all colours that aren’t red waldo = Import[“http://www.findwaldo.com/fankit/graphics/IntlManOfLiterature/Scenes/DepartmentStore.jpg”]; red = Fold[ImageSubtract, #[[1]], Rest[#]] &@ColorSeparate[waldo]; Next, I’m calculating the correlation of this image with a simple black and white pattern to find the red and white transitions in the shirt. corr = ImageCorrelate[red, Image@Join[ConstantArray[1, {2, … Read more