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return torch.tensor(boxes)\n\ndef encode(anchors,boxes):\n    ac=(anchors[:,:2]+anchors[:,2:])/2;aw=anchors[:,2:]-anchors[:,:2]\n    bc=(boxes[:,:2]+boxes[:,2:])/2;bw=boxes[:,2:]-boxes[:,:2]\n    return torch.cat([(bc-ac)/aw,torch.log((bw/aw).clamp(min=1e-6))],1)\n\ndef decode(anchors,offset):\n    ac=(anchors[:,:2]+anchors[:,2:])/2;aw=anchors[:,2:]-anchors[:,:2]\n    bc=ac+offset[:,:2]*aw;bw=aw*torch.exp(offset[:,2:].clamp(-3,3))\n    return torch.cat([bc-bw/2,bc+bw/2],1).clamp(0,1)\n\ndef match_targets(anchors,target):\n    \"\"\"-1 ignore, 0 background, 1/2 object. Each GT gets a distinct forced anchor.\"\"\"\n    classes=torch.zeros(len(anchors),dtype=torch.long);offsets=torch.zeros_like(anchors)\n    if not len(target['boxes']): return classes,offsets\n    overlap=iou_matrix(anchors,target['boxes']);best,best_gt=overlap.max(1)\n    classes[(best>=.25)&(best<.45)]=-1\n    positive=best>=.45\n    # Greedy global maximum, invalidate its anchor and GT; guarantees all GT assigned.\n    work=overlap.clone()\n    for _ in range(len(target['boxes'])):\n        flat=int(work.argmax()); a=flat//work.shape[1];g=flat%work.shape[1]\n        positive[a]=True;best_gt[a]=g;work[a,:]=-1;work[:,g]=-1\n    classes[positive]=target['labels'][best_gt[positive]]\n    offsets[positive]=encode(anchors[positive],target['boxes'][best_gt[positive]])\n    return classes,offsets\n\n\n```","sha256":"69910f0e843b76b0a9e207e1e13e524023bbfe037d0f6cd9c295e98abfdf64a5","chapter":{"id":"course","title":"哪些锚框受哪一种监督 · 实现代码"},"unit":{"id":"notebook-blocks/b6e5552805db40308895eb423c00fff1","title":"哪些锚框受哪一种监督 · 实现代码"},"page":{"id":"reading-opening","title":"哪些锚框受哪一种监督 · 实现代码","number":1},"sectionTitle":"哪些锚框受哪一种监督 · 实现代码","currentQuestion":"哪些锚框受哪一种监督 · 实现代码","sourceSlides":[],"knowledgeBlock":null,"formulas":[],"previousBlock":"b-2cb3a5d1df756dc74e175b19","nextBlock":null,"prerequisites":[{"id":"b-efd1394b129d9bb981ee180f","url":"#b-efd1394b129d9bb981ee180f","role":"section-title"},{"id":"b-63018cb325d1d1d81c6c4d23","url":"#b-63018cb325d1d1d81c6c4d23","role":"problem-context"}],"relatedBlocks":[]}]}