/**
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* implement some useful random-function
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*/
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/**
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* generates a random integer in [{@param inclusiveMin}; {@param exclusiveMax}).
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*
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* @param inclusiveMin {number}
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* @param exclusiveMax {number}
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*
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* @return {number} a random integer in [{@param inclusiveMin}; {@param exclusiveMax}).
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*
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*/
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export function uniform(inclusiveMin= 0, exclusiveMax) {
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let a = inclusiveMin,
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b = exclusiveMax;
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if (arguments.length === 1) { // only the first is set => there is no left bound
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a = 0;
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b = inclusiveMin;
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}
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if ( (b <= a) || (b-a) >= Number.MAX_VALUE ) {
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throw Error(`bad range [${a}, ${b})`)
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}
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return a + (Math.floor( (b-a)*Math.random() ));
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}
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/**
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* generates a random discrete distribution of a given probability of distribution
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* For example: given a probability of `[0.1, 0.3, 0.6]`, then the random generate number ist
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* one of 0 (with probability of 1%) , 1 (30%) and 2(60%).
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*
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* @param distribution {Array} an array of number, sum of its element must be at most 1
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* @return {number} an integer between 0 (include) and {@param distribution.length} (exclude)
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*
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* */
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export function discrete(distribution) {
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let sum = distribution.reduce( (acc,current) => acc + current);
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let dist = undefined;
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if(sum > 1) {
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throw Error(`bad distribution [${distribution}]`);
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} else if (sum < 1) {
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dist = [...distribution, 1 - sum];
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} else {
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dist = [...distribution];
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}
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let r = Math.random();
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let i = 0;
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let acc = dist[0];
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while(r >=acc ) {
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++i;
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acc += dist[i];
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}
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return i;
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}
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