numerical

Is there a simple function to round a Double or Float to a specified number of digits? I've searched here and on Hoogle (for (Fractional a) => Int -> a -> a ), but haven't found anything. Not sure whether any standard function exists, but you can do it this way: (fromInteger $ round $ f * (10^n)) / (10.0^^n) It depends on what you are going to do with the rounded number. If you want to use it in calculations, you should use Data.Decimal from Decimal library. If you want just to format the number nicely, you should use Text.Printf from the standard library ( base package). λ: ((/100) $

Say you have 100000000 32-bit floating point values in an array, and each of these floats has a value between 0.0 and 1.0. If you tried to sum them all up like this result = 0.0; for (i = 0; i < 100000000; i++) { result += array[i]; } you'd run into problems as result gets much larger than 1.0. So what are some of the ways to more accurately perform the summation? Sounds like you want to use Kahan Summation . According to Wikipedia, The Kahan summation algorithm (also known as compensated summation ) significantly reduces the numerical error in the total obtained by adding a sequence of finite

I have a function in Python: def f(x): return x[0]**3 + x[1]**2 + 7 # Actually more than this. # No analytical expression It's a scalar valued function of a vector. How can I approximate the Jacobian and Hessian of this function in numpy or scipy numerically? (Updated in late 2017 because there's been a lot of updates in this space.) Your best bet is probably automatic differentiation . There are now many packages for this, because it's the standard approach in deep learning: Autograd works transparently with most numpy code. It's pure-Python, requires almost no code changes for typical

I would like to generate a sequence of letters i.e. "A", "DE" "GJE", etc. that correspond to a number. The first 26 are pretty easy so 3 returns "C", 26 returns "Z", and 27 would return "AA", 28 "AB", and so on. The thing I can't quite figure out is how to do this so it will handle any number passed in. So if I pass in 4123 I should get back some combination of 3 letters since (26 * 26 * 26) allows for up to +17,000 combinations. Any suggestions? class Numeric Alph = ("a".."z").to_a def alph s, q = "", self (q, r = (q - 1).divmod(26)); s.prepend(Alph[r]) until q.zero? s end end 3.alph # => "c"

I have to switch from Python to C/C++. Do you know a quick "reference tutorial" or something like that to have a reference to how to start? For example something like the Numpy and Scipy tutorials. I have read a lot of "documentation", for example C++ for dummies the K&R C Programming Language a lot of blog and online documentation such as: http://eli.thegreenplace.net/2010/01/11/pointers-to-arrays-in-c/, http://newdata.box.sk/bx/c/ tons of Q&A here on StackOverflow ... but it's still not clear to me even how to do start porting to C/C++ something like: #!/usr/bin/env python import time import

I have a file with almost 900 lines in excel that I've saved as a tab deliminated .txt file. I'd like to sort the text file by the numbers given in the first column (they range between 0 and 2250). The other columns are both numbers and letters of varying length eg. myfile.txt: 0251 abcd 1234,24 bcde 2240 efgh 2345,98 ikgpppm 0001 lkjsi 879,09 ikol I've tried sort -k1 -n myfile.txt > myfile_num.txt but I just get an identical file with new name. I'd like to get: myfile_num.txt 0001 lkjsi 879,09 ikol 0251 abcd 1234,24 bcde 2240 efgh 2345,98 ikgpppm What am I doing wrong? I'm guessing that it's

This is actually a follow-up of this thread: Perl: Numerical sort of arrays in a hash I couldn't edit the original question because my current code is a bit different, so I'm just asking this as another question. Okay after using the Schwarzian Transform, I have this: my @mylines =("0.899 0.92 cat", "9.999 0.001 dog", "-0.52 0.3 humpty", "13.52 0.09 bumbo", "-1.52 0.98 nanny", "3.52 0.34 lala"); my @sorted = map { join ' ', @$_ } reverse sort { $a->[0] cmp $b->[0] or $a->[1] <=> $b->[1] } map { [ split ] } (@mylines); print "$_\n" for @sorted; I would expect the output to be sorted first by