swapRowsLU method Null safety
Swap rows in a matrix holding an LU decomposition.
Implementation
void swapRowsLU(int r1, int r2) {
assert(isLU);
checkIndices(r1, r2); // It's square, so this works
final swaps = _rowSwaps!;
final t = swaps[r1];
swaps[r1] = swaps[r2];
swaps[r2] = t;
}