419 lines
11 KiB
Text
419 lines
11 KiB
Text
title:: Randomness
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categories:: Random
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summary:: Randomness in SC
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related:: Reference/randomSeed
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As in any computer program, there are no "truly random" number generators in SC.
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They are pseudo-random, meaning they use very complex, but deterministic
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algorithms to generate sequences of numbers that are long enough and complicated enough
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to seem "random" for human beings. (i.e. the patterns are too complex for us to detect.)
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If you start a random number generator algorithm with the same "seed" number
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several times, you get the same sequence of random numbers.
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(See example below, randomSeed)
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section:: Create single random numbers
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subsection:: Between zero and <number>
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code::
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5.rand // evenly distributed.
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1.0.linrand // probability decreases linearly from 0 to <number>.
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::
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subsection:: Between -<number> and <number>
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code::
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5.0.rand2 // evenly distributed.
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10.bilinrand // probability is highest around 0,
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// decreases linearly toward +-<number>.
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1.0.sum3rand // quasi-gaussian, bell-shaped distribution.
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::
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subsection:: Within a given range
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code::
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rrand(24, 48) // linear distribution in the given range.
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exprand(0.01, 1) // exponential distribution;
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// both numbers must have the same sign.
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// (Note that the distribution of numbers is not exactly an exponential distribution,
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// since that would be unbounded: we might call it a logarithmic uniform distribution.)
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::
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subsection:: Test them multiple times with a do loop
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code::
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20.do({ 5.rand.postln; }); // evenly distributed
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20.do({ 1.0.linrand.postln; }); // probability decreases linearly from 0 to 1.0
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20.do({ 5.0.rand2.postln; }); // even
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20.do({ 10.bilinrand.postln; }); // probability is highest around 0,
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// decreases linearly toward +-<number>.
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20.do({ 1.0.sum3rand.postln; }); // quasi-gaussian, bell-shaped.
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::
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subsection:: Collect the results in an array
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code::
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Array.fill(10, { 1000.linrand }).postln;
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// or more compact:
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{ 1.0.sum3rand }.dup(100)
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// or:
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({ 1.0.sum3rand } ! 100)
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::
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subsection:: Seeding
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You can seed a random generator in order to repeat
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the same sequence of random numbers:
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code::
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(
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5.do({
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thisThread.randSeed = 4;
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Array.fill(10, { 1000.linrand}).postln;
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});
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)
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// Just to check, no seeding:
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(
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5.do({ Array.fill(10, { 1000.linrand }).postln; });
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)
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::
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See also link::Reference/randomSeed::.
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subsection:: Histograms
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Demonstrate the various statistical distributions visually, with histograms:
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code::
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Array.fill(500, { 1.0.rand }).plot("Sequence of 500x 1.0.rand");
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Array.fill(500, { 1.0.linrand }).plot("Sequence of 500x 1.0.linrand");
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Array.fill(500, { 1.0.sum3rand }).plot("Sequence of 500x 1.0.sum3rand");
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::
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Use a histogram to display how often each (integer)
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occurs in a collection of random numbers, :
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code::
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(
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var randomNumbers, histogram, maxValue = 500, numVals = 10000, numBins = 500;
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randomNumbers = Array.fill(numVals, { maxValue.rand; });
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histogram = randomNumbers.histo(numBins, 0, maxValue);
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histogram.plot("histogram for rand 0 - " ++ maxValue);
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)
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::
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A histogram for linrand:
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code::
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(
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var randomNumbers, histogram, maxValue = 500.0, numVals = 10000, numBins = 500;
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randomNumbers = Array.fill(numVals, { maxValue.linrand; });
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histogram = randomNumbers.histo(numBins, 0, maxValue);
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histogram.plot("histogram for linrand 0 - " ++ maxValue);
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)
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::
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A histogram for bilinrand:
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code::
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(
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var randomNumbers, histogram, minValue = -250, maxValue = 250, numVals = 10000, numBins = 500;
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randomNumbers = Array.fill(numVals, { maxValue.bilinrand; });
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histogram = randomNumbers.histo(numBins, minValue, maxValue);
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histogram.plot("histogram for bilinrand" + minValue + "to" + maxValue);
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)
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::
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A histogram for exprand:
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code::
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(
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var randomNumbers, histogram, minValue = 5.0, maxValue = 500, numVals = 10000, numBins = 500;
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randomNumbers = Array.fill(numVals, { exprand(minValue, maxValue); });
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histogram = randomNumbers.histo(numBins, minValue, maxValue);
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histogram.plot("histogram for exprand: " ++ minValue ++ " to " ++ maxValue);
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)
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::
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And for sum3rand (cheap quasi-gaussian):
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code::
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(
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var randomNumbers, histogram, minValue = -250, maxValue = 250, numVals = 10000, numBins = 500;
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randomNumbers = Array.fill(numVals, { maxValue.sum3rand; });
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histogram = randomNumbers.histo(numBins, minValue, maxValue);
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histogram.plot("histogram for sum3rand " ++ minValue ++ " to " ++ maxValue);
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)
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::
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subsection:: on Collections
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All of the single-number methods also work for (Sequenceable)Collections,
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simply by applying the given random message to each element of the collection:
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code::
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[ 1.0, 10, 100.0, \aSymbol ].rand.postln; // note: Symbols are left as they are.
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List[ 10, -3.0, \aSymbol ].sum3rand.postln;
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::
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subsection:: Arbitrary random distributions
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An integral table can be used to create an arbitrary random distribution quite efficiently. The table
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building is expensive though. The more points there are in the random table, the more accurate the
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distribution.
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code::
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(
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var randomNumbers, histogram, distribution, randomTable, randTableSize=200;
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var minValue = -250, maxValue = 250, numVals = 10000, numBins = 500;
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// create some random distribution with values between 0 and 1
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distribution = Array.fill(randTableSize,
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{ arg i; (i/ randTableSize * 35).sin.max(0) * (i / randTableSize) }
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);
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// render a randomTable
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randomTable = distribution.asRandomTable;
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// get random numbers, scale them
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randomNumbers = Array.fill(numVals, { randomTable.tableRand * (maxValue - minValue) + minValue; });
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histogram = randomNumbers.histo(numBins, minValue, maxValue);
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histogram.plot("this is the histogram we got");
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distribution.plot("this was the histogram we wanted");
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)
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::
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section:: Random decisions
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code:: coin :: simulates a coin toss and results in true or false.
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1.0 is always true, 0.0 is always false, 0.5 is 50:50 chance.
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code::
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20.do({ 0.5.coin.postln });
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::
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biased random decision can be simulated bygenerating a single value
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and check against a threshhold:
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code::
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20.do({ (1.0.linrand > 0.5).postln });
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20.do({ (exprand(0.05, 1.0) > 0.5).postln });
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::
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section:: Generating Collections of random numbers
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code::
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// size, minVal, maxVal
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Array.rand(7, 0.0, 1.0).postln;
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// is short for:
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Array.fill(7, { rrand(0.0, 1.0) }).postln;
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::
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code::
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// size, minVal, maxVal
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List.linrand(7, 10.0, 15.0).postln;
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// is short for:
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List.fill(7, { 10 + 5.0.linrand }).postln;
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::
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code::
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Signal.exprand(10, 0.1, 1);
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Signal.rand2(10, 1.0);
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::
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section:: Random choice from Collections
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code::choose:: : equal chance for each element.
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code::
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10.do({ [ 1, 2, 3 ].choose.postln });
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::
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Weighted choice:
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code::wchoose(weights):: : An array of weights sets the chance for each element.
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code::
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10.do({ [ 1, 2, 3 ].wchoose([0.1, 0.2, 0.7]).postln });
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::
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section:: Randomize the order of a Collection
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code::
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List[ 1, 2, 3, 4, 5 ].scramble.postln;
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::
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section:: Generate random numbers without duplicates
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code::
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f = { |n=8, min=0, max=7| (min..max).scramble.keep(n) };
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f.value(8, 0, 7)
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::
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section:: Randomly group a Collection
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code::
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curdle(probability)
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The probability argument sets the chance that two adjacent elements will be separated.
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code::
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[ 1, 2, 3, 4, 5, 6, 7, 8 ].curdle(0.2).postln; // big groups
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[ 1, 2, 3, 4, 5, 6, 7, 8 ].curdle(0.75).postln; // small groups
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::
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section:: Random signal generators, i.e. UGens
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list::
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## link::Classes/PinkNoise::
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## link::Classes/WhiteNoise::
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## link::Classes/GrayNoise::
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## link::Classes/BrownNoise::
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## link::Classes/ClipNoise::
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## link::Classes/LFNoise0::
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## link::Classes/LFNoise1::
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## link::Classes/LFNoise2::
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## link::Classes/LFClipNoise::
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## link::Classes/LFDNoise0::
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## link::Classes/LFDNoise1::
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## link::Classes/LFDNoise3::
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## link::Classes/LFDClipNoise::
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## link::Classes/Dust::
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## link::Classes/Dust2::
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## link::Classes/Crackle::
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## link::Classes/TWChoose::
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::
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Also see UGens>Generators>Stochastic in the link::Browse#UGens>Generators>Stochastic:: page.
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subsection:: Random operators on signals
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Unary or binary random method produce a random value for each frame (not implemented in some cases). This can be used to implement tendency masks.
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code::
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{ rrand(SinOsc.ar(0.1), SinOsc.ar(0.42)) * 0.1 }.play
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{ exprand(SinOsc.ar(0.1)) * 0.1 }.play
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{ linrand(SinOsc.ar(0.1)) * 0.1 }.play
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{ bilinrand(SinOsc.ar(0.1)) * 0.1 }.play
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{ sum3rand(SinOsc.ar(0.1)) * 0.1 }.play
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{ coin(SinOsc.ar(0.1)) * 0.1 }.play
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::
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subsection:: UGens that generate random numbers once, or on trigger:
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definitionlist::
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## link::Classes/Rand:: || uniform distribution of float between (lo, hi), as for numbers.
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## link::Classes/IRand:: || uniform distribution of integer numbers.
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## link::Classes/TRand:: || uniform distribution of float numbers, triggered
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## link::Classes/TIRand:: || uniform distribution of integer numbers, triggered
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## link::Classes/LinRand:: || skewed distribution of float numbers, triggered
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## link::Classes/NRand:: || sum of n uniform distributions, approximates gaussian distr. with higher n.
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## link::Classes/ExpRand:: || exponential distribution
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## link::Classes/TExpRand:: || exponential distribution, triggered
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## link::Classes/CoinGate:: || statistical gate for a trigger
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## link::Classes/TWindex:: || triggered weighted choice between a list.
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::
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subsection:: Seeding
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Like using randSeed to set the random generatorsfor each thread in sclang,
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you can choose which of several random generators on the server to use,
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and you can reset (seed) these random generators:
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list::
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## link::Classes/RandID::
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## link::Classes/RandSeed::
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::
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subsection:: UGens that generate random numbers on demand
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("Demand UGens")
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list::
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## link::Classes/Dwhite::
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## link::Classes/Dbrown::
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## link::Classes/Diwhite::
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## link::Classes/Dibrown::
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## link::Classes/Drand::
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## link::Classes/Dxrand::
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::
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see random patterns with analogous names
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section:: Random Patterns
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definitionlist::
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## link::Classes/Prand:: || choose randomly one from a list ( list, numRepeats)
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## link::Classes/Pxrand:: || choose one element from a list, no repeat of previous choice
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## link::Classes/Pwhite:: || within range [<hi>, <lo>], choose a random value.
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## link::Classes/Pbrown:: || within range [<hi>, <lo>], do a random walk with a maximum <step> to the next value.
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## link::Classes/Pgbrown:: || geometric brownian motion
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## link::Classes/Plprand::
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## link::Classes/Phprand::
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## link::Classes/Pmeanrand::
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## link::Classes/Pbeta::
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## link::Classes/Pcauchy::
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## link::Classes/Pgauss::
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## link::Classes/Ppoisson::
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## link::Classes/Pexprand::
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## link::Classes/Pwrand:: || choose from a list, probabilities by weights
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code::
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Pwrand([ 1, 2, 3 ], [0.1, 0.3, 0.6], 20);
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::
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## link::Classes/Pshuf:: || scramble the list, then repeat that order <repeats> times.
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## link::Classes/Pwalk:: || code::Pwalk( (0 .. 10), Prand([ -2,-1, 1, 2], inf));:: random walk.
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## link::Classes/Pfsm:: || random finite state machine pattern, see its help file. see also MarkovSet in MathLib quark
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## link::Classes/Pseed:: || sets the random seed for that stream.
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::
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some basic examples
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code::
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(
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Pbind(\note, Prand([ 0, 2, 4 ], inf),
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\dur, 0.2
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).play;
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)
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(
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Pbind(
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\note, Pxrand([ 0, 2, 4 ], inf),
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\dur, 0.2
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).play;
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)
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(
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Pbind(
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\note, Pwrand([ 0, 2, 4 ], [0.1, 0.3, 0.6], inf),
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\dur, 0.2
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).play;
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)
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(
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Pbind(
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\midinote, Pwhite(48, 72, inf),
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\dur, 0.2
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).play;
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)
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(
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Pbind(
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\midinote, Pbrown(48, 72, 5, inf),
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\dur, 0.2
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).play;
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)
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(
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Pbind(
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\midinote, Pgbrown(48, 72, 0.5, inf).round,
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\dur, 0.2
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).play;
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)
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::
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