vectorization
What is vectorization? [closed]
Python for loops are inherently slower than their C counterpart. This is why numpy offers vectorized actions on numpy arrays. It pushes the for loop you would usually do in Python down to the C level, which is much faster. numpy offers vectorized (“C level for loop”) alternatives to things that otherwise would need to … Read more
Comparing BSXFUN and REPMAT
Introduction The debate on whether bsxfun is better than repmat or vice versa has been going on like forever. In this post, we would try to compare how the different built-ins that ship with MATLAB fight it out against repmat equivalents in terms of their runtime performances and hopefully draw some meaningful conclusions out of … Read more
Converting BMP image to set of instructions for a plotter?
Dithering Well I got some time for this today so here the result. You did not provide your plotter color palette so I extracted it from your resulting images but you can use any. The idea behind dithering is simple our perception integrates color on area not individual pixels so you have to use some … Read more
Vectorized IF statement in R?
x <- seq(0.1,10,0.1) > x [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 [16] 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 [31] 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 4.3 4.4 4.5 [46] 4.6 … Read more
What is “vectorization”?
Many CPUs have “vector” or “SIMD” instruction sets which apply the same operation simultaneously to two, four, or more pieces of data. Modern x86 chips have the SSE instructions, many PPC chips have the “Altivec” instructions, and even some ARM chips have a vector instruction set, called NEON. “Vectorization” (simplified) is the process of rewriting … Read more
Why doesn’t gcc resolve _mm256_loadu_pd as single vmovupd?
GCC’s default tuning (-mtune=generic) includes -mavx256-split-unaligned-load and -mavx256-split-unaligned-store, because that gives a minor speedup on some CPUs (e.g. first-gen Sandybridge, and some AMD CPUs) in some cases when memory is actually misaligned at runtime. Use -O3 -mno-avx256-split-unaligned-load -mno-avx256-split-unaligned-store if you don’t want this, or better, use -mtune=haswell. Or use -march=native to optimize for your own … Read more
Split string column to create new binary columns
Using mtabuate from the qdapTools package that I maintain: library(qdapTools) mtabulate(strsplit(as.character(dat[[1]]), “https://stackoverflow.com/”)) ## V1 ca cbr_LBL cni_at.p3x.4 eq2_off eq2_on fe.gr hi.on hi.ov put sent_1 sent_1fe.gr ## 1 1 1 0 0 1 1 1 0 0 1 1 0 ## 2 1 1 0 0 1 1 1 1 1 1 1 0 ## 3 … Read more
Finding islands of zeros in a sequence
These are the steps I would take to solve your problem in a vectorized way, starting with a given vector sig: First, threshold the vector to get a vector tsig of zeros and ones (zeroes where the absolute value of the signal drops close enough to zero, ones elsewhere): tsig = (abs(sig) >= eps); %# … Read more
Why can’t R’s ifelse statements return vectors?
The documentation for ifelse states: ifelse returns a value with the same shape as test which is filled with elements selected from either yes or no depending on whether the element of test is TRUE or FALSE. Since you are passing test values of length 1, you are getting results of length 1. If you … Read more