| 415 | } |
| 416 | |
| 417 | QMatrix getFullOperatorMatrix( |
| 418 | int* ctrls, int numCtrls, int *targs, int numTargs, QMatrix op, int numQubits |
| 419 | ) { |
| 420 | DEMAND( numCtrls >= 0 ); |
| 421 | DEMAND( numTargs >= 0 ); |
| 422 | DEMAND( numQubits >= (numCtrls+numTargs) ); |
| 423 | DEMAND( op.size() == (1u << numTargs) ); |
| 424 | |
| 425 | // copy {ctrls} and {targs}to restore at end |
| 426 | vector<int> ctrlsCopy(ctrls, ctrls+numCtrls); |
| 427 | vector<int> targsCopy(targs, targs+numTargs); |
| 428 | |
| 429 | // full-state matrix of qubit swaps |
| 430 | QMatrix swaps = getIdentityMatrix(1 << numQubits); |
| 431 | QMatrix unswaps = getIdentityMatrix(1 << numQubits); |
| 432 | QMatrix matr; |
| 433 | |
| 434 | // swap targs to {0, ..., numTargs-1} |
| 435 | for (int i=0; i<numTargs; i++) { |
| 436 | if (i != targs[i]) { |
| 437 | matr = getSwapMatrix(i, targs[i], numQubits); |
| 438 | swaps = matr * swaps; |
| 439 | unswaps = unswaps * matr; |
| 440 | |
| 441 | // even if this is the last targ, ctrls might still need updating |
| 442 | updateIndices( |
| 443 | i, targs[i], (i < numTargs-1)? &targs[i+1] : NULL, |
| 444 | numTargs-i-1, ctrls, numCtrls); |
| 445 | } |
| 446 | } |
| 447 | |
| 448 | // swap ctrls to {numTargs, ..., numTargs+numCtrls-1} |
| 449 | for (int i=0; i<numCtrls; i++) { |
| 450 | int newInd = numTargs+i; |
| 451 | if (newInd != ctrls[i]) { |
| 452 | matr = getSwapMatrix(newInd, ctrls[i], numQubits); |
| 453 | swaps = matr * swaps; |
| 454 | unswaps = unswaps * matr; |
| 455 | |
| 456 | // update remaining ctrls (if any exist) |
| 457 | if (i < numCtrls-1) |
| 458 | updateIndices(newInd, ctrls[i], NULL, 0, &ctrls[i+1], numCtrls-i-1); |
| 459 | } |
| 460 | } |
| 461 | |
| 462 | // construct controlled-op matrix for qubits {0, ..., numCtrls+numTargs-1} |
| 463 | size_t dim = 1 << (numCtrls+numTargs); |
| 464 | QMatrix fullOp = getIdentityMatrix(dim); |
| 465 | setSubMatrix(fullOp, op, dim-op.size(), dim-op.size()); |
| 466 | |
| 467 | // create full-state controlled-op matrix (left-pad identities) |
| 468 | if (numQubits > numCtrls+numTargs) { |
| 469 | size_t pad = 1 << (numQubits - numCtrls - numTargs); |
| 470 | fullOp = getKroneckerProduct(getIdentityMatrix(pad), fullOp); |
| 471 | } |
| 472 | |
| 473 | // apply swap to either side (to swap qubits back and forth) |
| 474 | fullOp = unswaps * fullOp * swaps; |
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