public static Tensor symmetrize(SimpleTensor tensor, int[] freeIndices, Symmetries symmetries) {
if (symmetries.isEmpty()) return tensor;
int[] tempI = freeIndices.clone();
int[] allFreeIndices = tensor.getIndices().getFree().getAllIndices().copy();
Arrays.sort(tempI);
Arrays.sort(allFreeIndices);
int[] diff = MathUtils.intSetDifference(tempI, allFreeIndices);
System.arraycopy(freeIndices, 0, allFreeIndices, 0, freeIndices.length);
System.arraycopy(diff, 0, allFreeIndices, freeIndices.length, diff.length);
SumBuilder builder = new SumBuilder();
Tensor temp;
for (Symmetry symmetry : symmetries) {
temp =
applyIndexMapping(tensor, allFreeIndices, permute(allFreeIndices, symmetry), new int[0]);
if (symmetry.isAntiSymmetry()) temp = negate(temp);
builder.put(temp);
}
temp = builder.build();
if (temp instanceof Sum) {
// retrieving factor
Complex factor = null, tempF;
for (int i = temp.size() - 1; i >= 0; --i) {
if (temp.get(i) instanceof Product) {
tempF = ((Product) temp.get(i)).getFactor();
assert tempF.isInteger();
tempF = tempF.abs();
} else tempF = Complex.ONE;
if (factor == null) factor = tempF;
assert factor.equals(tempF);
}
if (!factor.isOne())
temp = FastTensors.multiplySumElementsOnFactor((Sum) temp, factor.reciprocal());
return multiply(new Complex(new Rational(1, temp.size())), temp);
}
return temp;
}
