/**
* Product two factors, taking the multiplication at the intersections.
*
* @param other the other factor to be multiplied
* @return a factor containing the union of both variable sets
*/
public TableFactor multiply(TableFactor other) {
// Calculate the result domain
List<Integer> domain = new ArrayList<>();
List<Integer> otherDomain = new ArrayList<>();
List<Integer> resultDomain = new ArrayList<>();
for (int n : neighborIndices) {
domain.add(n);
resultDomain.add(n);
}
for (int n : other.neighborIndices) {
otherDomain.add(n);
if (!resultDomain.contains(n)) resultDomain.add(n);
}
// Create result TableFactor
int[] resultNeighborIndices = new int[resultDomain.size()];
int[] resultDimensions = new int[resultNeighborIndices.length];
for (int i = 0; i < resultDomain.size(); i++) {
int var = resultDomain.get(i);
resultNeighborIndices[i] = var;
// assert consistency about variable size, we can't have the same variable with two different
// sizes
assert ((getVariableSize(var) == 0 && other.getVariableSize(var) > 0)
|| (getVariableSize(var) > 0 && other.getVariableSize(var) == 0)
|| (getVariableSize(var) == other.getVariableSize(var)));
resultDimensions[i] =
Math.max(
getVariableSize(resultDomain.get(i)), other.getVariableSize(resultDomain.get(i)));
}
TableFactor result = new TableFactor(resultNeighborIndices, resultDimensions);
// OPTIMIZATION:
// If we're a factor of size 2 receiving a message of size 1, then we can optimize that pretty
// heavily
// We could just use the general algorithm at the end of this set of special cases, but this is
// the fastest way
if (otherDomain.size() == 1 && (resultDomain.size() == domain.size()) && domain.size() == 2) {
int msgVar = otherDomain.get(0);
int msgIndex = resultDomain.indexOf(msgVar);
if (msgIndex == 0) {
for (int i = 0; i < resultDimensions[0]; i++) {
double d = other.values[i];
int k = i * resultDimensions[1];
for (int j = 0; j < resultDimensions[1]; j++) {
int index = k + j;
result.values[index] = values[index] + d;
}
}
} else if (msgIndex == 1) {
for (int i = 0; i < resultDimensions[0]; i++) {
int k = i * resultDimensions[1];
for (int j = 0; j < resultDimensions[1]; j++) {
int index = k + j;
result.values[index] = values[index] + other.values[j];
}
}
}
}
// OPTIMIZATION:
// The special case where we're a message of size 1, and the other factor is receiving the
// message, and of size 2
else if (domain.size() == 1
&& (resultDomain.size() == otherDomain.size())
&& resultDomain.size() == 2) {
return other.multiply(this);
}
// Otherwise we follow the big comprehensive, slow general purpose algorithm
else {
// Calculate back-pointers from the result domain indices to original indices
int[] mapping = new int[result.neighborIndices.length];
int[] otherMapping = new int[result.neighborIndices.length];
for (int i = 0; i < result.neighborIndices.length; i++) {
mapping[i] = domain.indexOf(result.neighborIndices[i]);
otherMapping[i] = otherDomain.indexOf(result.neighborIndices[i]);
}
// Do the actual joining operation between the two tables, applying 'join' for each result
// element.
int[] assignment = new int[neighborIndices.length];
int[] otherAssignment = new int[other.neighborIndices.length];
// OPTIMIZATION:
// Rather than use the standard iterator, which creates lots of int[] arrays on the heap,
// which need to be GC'd,
// we use the fast version that just mutates one array. Since this is read once for us here,
// this is ideal.
Iterator<int[]> fastPassByReferenceIterator = result.fastPassByReferenceIterator();
int[] resultAssignment = fastPassByReferenceIterator.next();
while (true) {
// Set the assignment arrays correctly
for (int i = 0; i < resultAssignment.length; i++) {
if (mapping[i] != -1) assignment[mapping[i]] = resultAssignment[i];
if (otherMapping[i] != -1) otherAssignment[otherMapping[i]] = resultAssignment[i];
}
result.setAssignmentLogValue(
resultAssignment,
getAssignmentLogValue(assignment) + other.getAssignmentLogValue(otherAssignment));
// This mutates the resultAssignment[] array, rather than creating a new one
if (fastPassByReferenceIterator.hasNext()) fastPassByReferenceIterator.next();
else break;
}
}
return result;
}
/**
* Marginalizes out a variable by applying an associative join operation for each possible
* assignment to the marginalized variable.
*
* @param variable the variable (by 'name', not offset into neighborIndices)
* @param startingValue associativeJoin is basically a foldr over a table, and this is the
* initialization
* @param curriedFoldr the associative function to use when applying the join operation, taking
* first the assignment to the value being marginalized, and then a foldr operation
* @return a new TableFactor that doesn't contain 'variable', where values were gotten through
* associative marginalization.
*/
private TableFactor marginalize(
int variable,
double startingValue,
BiFunction<Integer, int[], BiFunction<Double, Double, Double>> curriedFoldr) {
// Can't marginalize the last variable
assert (getDimensions().length > 1);
// Calculate the result domain
List<Integer> resultDomain = new ArrayList<>();
for (int n : neighborIndices) {
if (n != variable) {
resultDomain.add(n);
}
}
// Create result TableFactor
int[] resultNeighborIndices = new int[resultDomain.size()];
int[] resultDimensions = new int[resultNeighborIndices.length];
for (int i = 0; i < resultDomain.size(); i++) {
int var = resultDomain.get(i);
resultNeighborIndices[i] = var;
resultDimensions[i] = getVariableSize(var);
}
TableFactor result = new TableFactor(resultNeighborIndices, resultDimensions);
// Calculate forward-pointers from the old domain to new domain
int[] mapping = new int[neighborIndices.length];
for (int i = 0; i < neighborIndices.length; i++) {
mapping[i] = resultDomain.indexOf(neighborIndices[i]);
}
// Initialize
for (int[] assignment : result) {
result.setAssignmentLogValue(assignment, startingValue);
}
// Do the actual fold into the result
int[] resultAssignment = new int[result.neighborIndices.length];
int marginalizedVariableValue = 0;
// OPTIMIZATION:
// Rather than use the standard iterator, which creates lots of int[] arrays on the heap, which
// need to be GC'd,
// we use the fast version that just mutates one array. Since this is read once for us here,
// this is ideal.
Iterator<int[]> fastPassByReferenceIterator = fastPassByReferenceIterator();
int[] assignment = fastPassByReferenceIterator.next();
while (true) {
// Set the assignment arrays correctly
for (int i = 0; i < assignment.length; i++) {
if (mapping[i] != -1) resultAssignment[mapping[i]] = assignment[i];
else marginalizedVariableValue = assignment[i];
}
result.setAssignmentLogValue(
resultAssignment,
curriedFoldr
.apply(marginalizedVariableValue, resultAssignment)
.apply(
result.getAssignmentLogValue(resultAssignment),
getAssignmentLogValue(assignment)));
if (fastPassByReferenceIterator.hasNext()) fastPassByReferenceIterator.next();
else break;
}
return result;
}
/**
* Marginalize out a variable by taking a sum.
*
* @param variable the variable to be summed out
* @return a factor with variable removed
*/
public TableFactor sumOut(int variable) {
// OPTIMIZATION: This is by far the most common case, for linear chain inference, and is worth
// making fast
// We can use closed loops, and not bother with using the basic iterator to loop through
// indices.
// If this special case doesn't trip, we fall back to the standard (but slower) algorithm for
// the general case
if (getDimensions().length == 2) {
if (neighborIndices[0] == variable) {
TableFactor marginalized =
new TableFactor(new int[] {neighborIndices[1]}, new int[] {getDimensions()[1]});
for (int i = 0; i < marginalized.values.length; i++) marginalized.values[i] = 0;
// We use the stable log-sum-exp trick here, so first we calculate the max
double[] max = new double[getDimensions()[1]];
for (int j = 0; j < getDimensions()[1]; j++) {
max[j] = Double.NEGATIVE_INFINITY;
}
for (int i = 0; i < getDimensions()[0]; i++) {
int k = i * getDimensions()[1];
for (int j = 0; j < getDimensions()[1]; j++) {
int index = k + j;
if (values[index] > max[j]) {
max[j] = values[index];
}
}
}
// Then we take the sum, minus the max
for (int i = 0; i < getDimensions()[0]; i++) {
int k = i * getDimensions()[1];
for (int j = 0; j < getDimensions()[1]; j++) {
int index = k + j;
if (Double.isFinite(max[j])) {
marginalized.values[j] += Math.exp(values[index] - max[j]);
}
}
}
// And now we exponentiate, and add back in the values
for (int j = 0; j < getDimensions()[1]; j++) {
if (Double.isFinite(max[j])) {
marginalized.values[j] = max[j] + Math.log(marginalized.values[j]);
} else {
marginalized.values[j] = max[j];
}
}
return marginalized;
} else {
assert (neighborIndices[1] == variable);
TableFactor marginalized =
new TableFactor(new int[] {neighborIndices[0]}, new int[] {getDimensions()[0]});
for (int i = 0; i < marginalized.values.length; i++) marginalized.values[i] = 0;
// We use the stable log-sum-exp trick here, so first we calculate the max
double[] max = new double[getDimensions()[0]];
for (int i = 0; i < getDimensions()[0]; i++) {
max[i] = Double.NEGATIVE_INFINITY;
}
for (int i = 0; i < getDimensions()[0]; i++) {
int k = i * getDimensions()[1];
for (int j = 0; j < getDimensions()[1]; j++) {
int index = k + j;
if (values[index] > max[i]) {
max[i] = values[index];
}
}
}
// Then we take the sum, minus the max
for (int i = 0; i < getDimensions()[0]; i++) {
int k = i * getDimensions()[1];
for (int j = 0; j < getDimensions()[1]; j++) {
int index = k + j;
if (Double.isFinite(max[i])) {
marginalized.values[i] += Math.exp(values[index] - max[i]);
}
}
}
// And now we exponentiate, and add back in the values
for (int i = 0; i < getDimensions()[0]; i++) {
if (Double.isFinite(max[i])) {
marginalized.values[i] = max[i] + Math.log(marginalized.values[i]);
} else {
marginalized.values[i] = max[i];
}
}
return marginalized;
}
} else {
// This is a little tricky because we need to use the stable log-sum-exp trick on top of our
// marginalize
// dataflow operation.
// First we calculate all the max values to use as pivots to prevent overflow
TableFactor maxValues = maxOut(variable);
// Then we do the sum against an offset from the pivots
TableFactor marginalized =
marginalize(
variable,
0,
(marginalizedVariableValue, assignment) ->
(a, b) -> a + Math.exp(b - maxValues.getAssignmentLogValue(assignment)));
// Then we factor the max values back in, and
for (int[] assignment : marginalized) {
marginalized.setAssignmentLogValue(
assignment,
maxValues.getAssignmentLogValue(assignment)
+ Math.log(marginalized.getAssignmentLogValue(assignment)));
}
return marginalized;
}
}
