71 lines
1.9 KiB
Go
71 lines
1.9 KiB
Go
package simulation
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import (
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"fmt"
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"math/rand"
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)
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// TransitionMatrix is _almost_ a left stochastic matrix. It is technically
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// not one due to not normalizing the column values. In the future, if we want
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// to find the steady state distribution, it will be quite easy to normalize
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// these values to get a stochastic matrix. Floats aren't currently used as
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// the default due to non-determinism across architectures
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type TransitionMatrix struct {
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weights [][]int
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// total in each column
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totals []int
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n int
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}
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// CreateTransitionMatrix creates a transition matrix from the provided weights.
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// TODO: Provide example usage
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func CreateTransitionMatrix(weights [][]int) (TransitionMatrix, error) {
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n := len(weights)
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for i := 0; i < n; i++ {
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if len(weights[i]) != n {
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return TransitionMatrix{},
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fmt.Errorf("transition matrix: non-square matrix provided, error on row %d", i)
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}
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}
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totals := make([]int, n)
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for row := 0; row < n; row++ {
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for col := 0; col < n; col++ {
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totals[col] += weights[row][col]
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}
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}
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return TransitionMatrix{weights, totals, n}, nil
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}
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// NextState returns the next state randomly chosen using r, and the weightings
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// provided in the transition matrix.
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func (t TransitionMatrix) NextState(r *rand.Rand, i int) int {
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randNum := r.Intn(t.totals[i])
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for row := 0; row < t.n; row++ {
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if randNum < t.weights[row][i] {
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return row
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}
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randNum -= t.weights[row][i]
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}
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// This line should never get executed
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return -1
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}
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// GetMemberOfInitialState takes an initial array of weights, of size n.
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// It returns a weighted random number in [0,n).
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func GetMemberOfInitialState(r *rand.Rand, weights []int) int {
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n := len(weights)
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total := 0
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for i := 0; i < n; i++ {
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total += weights[i]
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}
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randNum := r.Intn(total)
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for state := 0; state < n; state++ {
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if randNum < weights[state] {
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return state
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}
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randNum -= weights[state]
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}
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// This line should never get executed
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return -1
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}
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