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• values from different fields in matalb

  - by ariel

  Hi does anybody familiar with a way that I could implement a matrix with values from a field (not the real or complex number, but lets say Z mod p). so I could perform all the operation of matlab on the matrix (with the values of the chosen field) Ariel

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• Flipping issue when interpolating Rotations using Quaternions

  - by uhuu

  I use slerp to interpolate between two quaternions representing rotations. The resulting rotation is then extracted as Euler angles to be fed into a graphics lib. This kind of works, but I have the following problem; when rotating around two (one works just fine) axes in the direction of the green arrow as shown in the left frame here the rotation soon jumps around to rotate from the opposite site to the opposite visual direction, as indicated by the red arrow in the right frame. This may be logical from a mathematical perspective (although not to me), but it is undesired. How could I achieve an interpolation with no visual flipping and changing of directions when rotating around more than one axis, following the green arrow at all times until the interpolation is complete? Thanks in advance.

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• How to make scipy.interpolate give a an extrapolated result beyond the input range?

  - by Salim Fadhley

  I'm trying to port a program which uses a hand-rolled interpolator (developed by a mathematitian colleage) over to use the interpolators provided by scipy. I'd like to use or wrap the scipy interpolator so that it has as close as possible behavior to the old interpolator. A key difference between the two functions is that in our original interpolator - if the input value is above or below the input range, our original interpolator will extrapolate the result. If you try this with the scipy interpolator it raises a ValueError. Consider this program as an example: import numpy as np from scipy import interpolate x = np.arange(0,10) y = np.exp(-x/3.0) f = interpolate.interp1d(x, y) print f(9) print f(11) # Causes ValueError, because it's greater than max(x) Is there a sensible way to make it so that instead of crashing, the final line will simply do a linear extrapolate, continuing the gradients defined by the first and last two pouints to infinity. Note, that in the real software I'm not actually using the exp function - that's here for illustration only!

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• How to compute the dot product?

  - by WizardOfOdds

  I have the following piece of pseudo-C/Java/C# code: int a[]= { 30, 20 }; int b[] = { 40, 50 }; int c[] = {12, 12}; How do I compute the sign of the dot-product AB . AC? I'm only interested in the sign, so I have: boolean signABxAC = ? Now concretely what do I write to get the sign of the dot-product AB . AC?

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• How can I write a power function myself?

  - by Koning WWWWWWWWWWWWWWWWWWWWWWW

  Since I was 12, I was always wondering how I can make a function which calculates the power (e.g. 23) myself. In most languages these are included in the standard library, mostly as pow(double x, double y), but how can I write it myself? I was thinking about for loops, but it think my brain got in a loop (when I wanted to do a power with a non-integer exponent, like 54.5 or negatives 2-21) and I went crazy ;) So, how can I write a function which calculates the power of a real number? Thanks

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• st-ordering library function?

  - by chang

  I'm in the search for an implementation of an ear-decomposition algorithm (http://www.ics.uci.edu/~eppstein/junkyard/euler/ear.html). I examined networkx and didn't find one. Although the algorithm layout is vaguely in my mind, I'd like to see some reference implementation, too. Side problem: First step could be an st-ordering of a graph. Are there any implementations for st-ordering algorithms you know? Thanks for your input. I'd really like to contribute e.g. to networkx by implementing the ear-decomposition algorithm in python.

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• inverse relationships

  - by Evan

  Give an example of data that would have an inverse relationship

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• How to compute the cross-product?

  - by WizardOfOdds

  I have the following piece of pseudo-C/Java/C# code: int a[]= { 30, 20 }; int b[] = { 40, 50 }; int c[] = {12, 12}; How do I compute the cross-product ABxAC?

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• Evaluating mathematical expressions in Python

  - by vander

  Hi, I want to tokenize a given mathematical expression into a binary tree like this: ((3 + 4 - 1) * 5 + 6 * -7) / 2 '/' / \ + 2 / \ * * / \ / \ - 5 6 -7 / \ + 1 / \ 3 4 Is there any pure Python way to do this? Like passing as a string to Python and then get back as a tree like mentioned above. Thanks.

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• How to get bit rotation function to accept any bit size?

  - by calccrypto

  i have these 2 functions i got from some other code def ROR(x, n): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (32 - n)) def ROL(x, n): return ROR(x, 32 - n) and i wanted to use them in a program, where 16 bit rotations are required. however, there are also other functions that require 32 bit rotations, so i wanted to leave the 32 in the equation, so i got: def ROR(x, n, bits = 32): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (bits - n)) def ROL(x, n, bits = 32): return ROR(x, bits - n) however, the answers came out wrong when i tested this set out. yet, the values came out correctly when the code is def ROR(x, n): mask = (2L**n) - 1 mask_bits = x & mask return (x >> n) | (mask_bits << (16 - n)) def ROL(x, n,bits): return ROR(x, 16 - n) what is going on and how do i fix this?

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• Finding the Formula for a Curve

  - by Mystagogue

  Is there a program that will take "response curve" values from me, and provide a formula that approximates the response curve? It would be cool if such a program would take a numeric "percent correct" (perhaps with a standard deviation) so that it returns simplified formulas when laxity is permissable, and more precise (viz. complex) formulas when the curve needs to be approximated closely. My interest is to play with the response curve values and "laxity" factor, until such a tool spits out a curve-fit formula simple enough that I know it will be high performance during machine computations.

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• adding up value of array and getting the average

  - by sea_1987

  I have an array that looks similar to this, [4] => Common_Model Object ( [id] => 4 [name] => [date_created] => [last_updated] => [user_id_updated] => [_table] => [_aliases] => Array ( [id] => 4 [name] => [date_created] => [date_updated] => [user_id_updated] => [rating] => 3 [recipe_id] => 5 ) [_nonDBAliases] => Array ( ) [_default] => Array ( ) [_related] => Array ( ) [_enums] => [_alsoDelete] => Array ( ) [_readOnly] => Array ( [0] => date_updated ) [_valArgs] => Array ( ) [_valArgsHash] => Array ( [default] => Array ( ) ) [_valAliases] => Array ( ) [_extraData] => Array ( ) [_inputs] => Array ( ) [_tableName] => jm_ratings [_tablePrefix] => [_niceDateUpdated] => 1st Jan 70 [_niceDateCreated] => 1st Jan 70 [_fetchAdminData] => [_mCache] => [_assets] => Array ( ) ) [3] => Common_Model Object ( [id] => 3 [name] => [date_created] => [last_updated] => [user_id_updated] => [_table] => [_aliases] => Array ( [id] => 3 [name] => [date_created] => [date_updated] => [user_id_updated] => [rating] => 1 [recipe_id] => 5 ) [_nonDBAliases] => Array ( ) [_default] => Array ( ) [_related] => Array ( ) [_enums] => [_alsoDelete] => Array ( ) [_readOnly] => Array ( [0] => date_updated ) [_valArgs] => Array ( ) [_valArgsHash] => Array ( [default] => Array ( ) ) [_valAliases] => Array ( ) [_extraData] => Array ( ) [_inputs] => Array ( ) [_tableName] => jm_ratings [_tablePrefix] => [_niceDateUpdated] => 1st Jan 70 [_niceDateCreated] => 1st Jan 70 [_fetchAdminData] => [_mCache] => [_assets] => Array ( ) ) [2] => Common_Model Object ( [id] => 2 [name] => [date_created] => [last_updated] => [user_id_updated] => [_table] => [_aliases] => Array ( [id] => 2 [name] => [date_created] => [date_updated] => [user_id_updated] => [rating] => 1 [recipe_id] => 5 ) [_nonDBAliases] => Array ( ) [_default] => Array ( ) [_related] => Array ( ) [_enums] => [_alsoDelete] => Array ( ) [_readOnly] => Array ( [0] => date_updated ) [_valArgs] => Array ( ) [_valArgsHash] => Array ( [default] => Array ( ) ) [_valAliases] => Array ( ) [_extraData] => Array ( ) [_inputs] => Array ( ) [_tableName] => jm_ratings [_tablePrefix] => [_niceDateUpdated] => 1st Jan 70 [_niceDateCreated] => 1st Jan 70 [_fetchAdminData] => [_mCache] => [_assets] => Array ( ) ) I wanting to add up the [rating] and get the mean average. But I dont know how do this with PHP, my attempt looks like this, <?php foreach ($rt as $rating) { $total = $rating->rating + $rating->rating } $total / count($rt); ?>

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• Python - How to find a correlation between two vectors ?

  - by psihodelia

  Given two vectors X and Y I have to find their correlation, i.e. their linear dependence/independence. Both vectors have equal dimension. A resulted answer should be a floating point number from [-1.0 .. 1.0]. Example: X=[-1, 2, 0] Y=[ 4, 2, -0.3] Find y=cor(X,Y) such that y belongs to [-1.0 .. 1.0]. It should be a simple construction involving a list-comprehension. No external library is allowed. UPDATE: ok, if dot product is enough, then here is my solution: nX = 1/(sum([x*x for x in X]) ** 0.5) nY = 1/(sum([y*y for y in Y]) ** 0.5) cor = sum([(x*nX)*(y*nY) for x,y in zip(X,Y) ]) right?

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• Calculating rotation in > 360 deg. situations

  - by danglebrush

  I'm trying to work out a problem I'm having with degrees. I have data that is a list of of angles, in standard degree notation -- e.g. 26 deg. Usually when dealing with angles, if an angle exceeds 360 deg then the angle continues around and effectively "resets" -- i.e. the angle "starts again", e.g. 357 deg, 358 deg, 359 deg, 0 deg, 1 deg, etc. What I want to happen is the degree to continue increasing -- i.e. 357 deg, 358 deg, 359 deg, 360 deg, 361 deg, etc. I want to modify my data so that I have this converted data in it. When numbers approach the 0 deg limit, I want them to become negative -- i.e. 3 deg, 2 deg, 1 deg, 0 deg, -1 deg, -2 deg, etc. With multiples of 360 deg (both positive and negative), I want the degrees to continue, e.g. 720 deg, etc. Any suggestions on what approach to take? There is, no doubt, a frustratingly simple way of doing this, but my current solution is kludgey to say the least .... ! My best attempt to date is to look at the percentage difference between angle n and angle n - 1. If this is a large difference -- e.g. 60% -- then this needs to be modified, by adding or subtracting 360 deg to the current value, depending on the previous angle value. That is, if the previous angle is negative, substract 360, and add 360 if the previous angle is positive. Any suggestions on improving this? Any improvements?

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• Interview Q: find angle between hour and minute hands in an analog clock

  - by polygenelubricants

  I was given this interview question recently: An analog clock shows that the current time is HH:MM. Compute in degree, the smaller angle between the hour and minute hands. Be as precise as you can. I'm wondering what's the simplest, most readable, most precise algorithm is. Solution in any language is welcome (but do explain it a bit if you think it's necessary).

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• Solving simultaneous equations

  - by Milo

  Here is my problem: Given x, y, z and ratio where z is known and ratio is known and is a float representing a relative value, I need to find x and y. I know that: x / y == ratio y - x == z What I'm trying to do is make my own scroll pane and I'm figuring out the scrollbar parameters. So for example, If the scrollbar must be able to scroll 100 values (z) and the thumb must consume 80% of the bar (ratio = 0.8) then x would be 400 and y would be 500. Thanks

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• Looking for C# framework for plotting scientific data: 2d/3d ...

  - by Ivan

  I need to visualize some scientific calculations. I generally prefer reusing code if there is already a good available instead of inventing wheels each time, that's why I am asking. I need a C# code to draw charts (just outputting a bitmap is ok) of 2d (y=f(x)) and 3d (z=f(x,y)) digital data sets (where any axis can be float, int or datetime), sometimes combined. If I go here and click 3D in the navigation bar on the left, there I can see what I need. But the cheapest version costs $759 there, looks scary for a hobby project of an east-european student :-(

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• Need some help understanding this problem

  - by Legend

  I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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• Generate RTT values

  - by Jean Gauthier

  Hi all, I'm writing a Java applet where I should be able to simulate a connection between two hosts. Hence I have to generate packet round-trip times at random. These RTTs can go from ~0 to infinity, but are typically oscillating around some average value (i.e. an extremely large or small value is very improbable but possible). I was wondering if anyone had an idea of how I could do this? Thanks in advance

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• Ruby BigDecimal sanity check (floating point newb)

  - by Andy

  Hello, Hoping to get some feedback from someone more experienced here. I haven't dealt with the dreaded floating-point calculation before... Is my understanding correct that with Ruby BigDecimal types (even with varying precision and scale lengths) should calculate accurately or should I anticipate floating point shenanigans? All my values within a Rails application are BigDecimal type and I'm seeing some errors (they do have different decimal lengths), hoping it's just my methods and not my object types... Thanks!

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• Is there any valid reason radians are used as the inputs to trig function in many modern languages?

  - by johnmortal

  Is there any pressing reason trig functions should use radian inputs in modern programming languages? As far as I know radians are typically ugly to deal with except in three cases: (1) You want to compute an arc length and you know the angle of the arc and (2) You need to do symbolic calculus with trig functions (3) certain infinite series expansion look prettier if the input is in radians. None of these scenarios seem like a worthy justification for every programming language I am familiar with using radian inputs for Sin, Cos, Tangent, etc... The third one sounds good because it might mean one gets faster computations using radians (very slightly faster- the cost of one additional floating point multiplication ) , but I am dubious even of that because most commonly the developer had to take an extra step to put the angle in radians in the first place. The other two are ridiculous justifications for all the added obscurity.

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• Express any number as the sum of 4 prime numbers [Doubts]

  - by WarDoGG

  I was give a problem to express any number as sum of 4 prime numbers. Conditions: Not allowed to use any kind of database. Maximum execution time : 3 seconds Numbers only till 100,000 If the splitting is NOT possible, then return -1 What i did : using the sieve of eratosthenes, i calculated all prime numbers till the specified number. looked up a concept called goldbach conjecture which expresses an even number as the summation of 2 primes. However, i am stuck beyond that. Can anyone help me on this one as to what approach u might take ? The sieve of eratosthenes is taking 2 seconds to count primes till 100,000 :(((

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• How would I find all sets of N single-digit, non-repeating numbers that add up to a given sum in PHP

  - by TerranRich

  Let's say I want to find all sets of 5 single-digit, non-repeating numbers that add up to 30... I'd end up with [9,8,7,5,1], [9,8,7,4,2], [9,8,6,4,3], [9,8,6,5,2], [9,7,6,5,3], and [8,7,6,5,4]. Each of those sets contains 5 non-repeating digits that add up to 30, the given sum. Any help would be greatly appreciated. Even just a starting point for me to use would be awesome. I came up with one method, which seems like a long way of going about it: get all unique 5-digit numbers (12345, 12346, 12347, etc.), add up the digits, and see if it equals the given sum (e.g. 30). If it does, add it to the list of possible matching sets. I'm doing this for a personal project, which will help me in solving Kakuro puzzles without actually solving the whole thing at once. Yeah, it may be cheating, but it's... it's not THAT bad... :P

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• Base 62 conversion in Python

  - by mikl

  How would you convert an integer to base 62 (like hexadecimal, but with these digits: '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'). I have been trying to find a good Python library for it, but they all seems to be occupied with converting strings. The Python base64 module only accepts strings and turns a single digit into four characters. I was looking for something akin to what URL shorteners use.

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• How do I find the largest factor of an integer in mysql

  - by Bill H

  I am trying to write a select query that will dynamically determine the minimum number of items that can be packaged together. I am having trouble with one part of the query. ... CASE WHEN (pid.product_id) THEN 1 WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 11 = 0)) THEN CEILING(p.inner_pack / 11) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 7 = 0)) THEN CEILING(p.inner_pack / 7) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 6 = 0)) THEN CEILING(p.inner_pack / 6) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 5 = 0)) THEN CEILING(p.inner_pack / 5) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 4 = 0)) THEN CEILING(p.inner_pack / 4) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 3 = 0)) THEN CEILING(p.inner_pack / 3) WHEN ((p.case_pack = p.inner_pack) AND (p.inner_pack % 2 = 0)) THEN CEILING(p.inner_pack / 2) ELSE p.inner_pack END AS min_pack ... What I want to do is find the largest factorial of an integer (p.inner_pack) that is under 12. Is there a better way to do this in mysql?

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