{"id":36,"date":"2024-09-10T07:27:43","date_gmt":"2024-09-09T23:27:43","guid":{"rendered":"http:\/\/chaixiangyu.cn\/?p=36"},"modified":"2024-09-11T21:40:23","modified_gmt":"2024-09-11T13:40:23","slug":"armadillo%e4%bd%bf%e7%94%a8%e4%bb%8b%e7%bb%8d%ef%bc%88%e5%8d%81%e4%ba%8c%ef%bc%89%ef%bc%9afft-ifft","status":"publish","type":"post","link":"https:\/\/chaixiangyu.cn\/?p=36","title":{"rendered":"Armadillo\u4f7f\u7528\u4ecb\u7ecd\uff08\u5341\u4e8c\uff09\uff1afft \/ ifft"},"content":{"rendered":"\n

fft \/ ifft<\/h1>\n\n\n\n

\u7528\u9014\uff1afft \/ ifft\u51fd\u6570\u7528\u4e8e\u4e00\u7ef4\u5feb\u901f\u5085\u91cc\u53f6\u53d8\u6362\/\u5feb\u901f\u5085\u91cc\u53f6\u9006\u53d8\u6362<\/em>\u3002
\u8be5\u51fd\u6570\u91cd\u8f7d\u6709cx_mat Y = fft( X )\u3001cx_mat Y = fft( X, n )\u3001cx_mat Z = ifft( cx_mat Y )\u3001cx_mat Z = ifft( cx_mat Y, n )
\u7c7b\u578b\uff1a\u666e\u901a\u51fd\u6570<\/em>
\u96b6\u5c5e\uff1aSignal & Image Processing<\/em><\/p>\n\n\n\n

1\u3001fft()<\/em>: fast Fourier transform of a vector or matrix (real or complex)<\/p>\n\n\n\n

2\u3001ifft()<\/em>: inverse fast Fourier transform of a vector or matrix (complex only)<\/p>\n\n\n\n

3\u3001If given a matrix, the transform is done on each column vector of the matrix<\/p>\n\n\n\n

4\u3001The optional n<\/em> argument specifies the transform length:
\u2003 \u2003 if n<\/em> is larger than the length of the input vector, a zero-padded version of the vector is used
\u2003 \u2003 if n<\/em> is smaller than the length of the input vector, only the first n<\/em> elements of the vector are used<\/p>\n\n\n\n

5\u3001If n<\/em> is not specified, the transform length is the same as the length of the input vector<\/p>\n\n\n\n

6\u3001\u6ce8\u610f:<\/strong> the transform is fastest when the transform length is a power of 2<\/code>, eg. 64, 128, 256, 512, 1024, ...<\/code><\/p>\n\n\n\n

7\u3001The implementation of the transform in this version is preliminary; it is not yet fully optimised<\/p>\n\n\n\n

\u793a\u4f8b\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n\n\n\n

    vec X = randu<vec>(10);\n    cx_vec Y = fft(X, 8);\n    cx_vec Z = ifft(Y, 8);\n\n    X.print(\"X:\");\n    Y.print(\"Y:\");\n    Z.print(\"Z:\");<\/code><\/pre>\n\n\n\n
\u8fd0\u884c\u7ed3\u679c\uff1a<\/p>\n\n\n\n
Armadillo version: 9.900.1 (Nocturnal Misbehaviour)\nX:\n   0.0013\n   0.1933\n   0.5850\n   0.3503\n   0.8228\n   0.1741\n   0.7105\n   0.3040\n   0.0914\n   0.1473\nY:\n  (+3.141e+000,+0.000e+000)\n  (-8.408e-001,+7.916e-002)\n  (-4.714e-001,+2.868e-001)\n  (-8.024e-001,-1.718e-001)\n  (+1.098e+000,+0.000e+000)\n  (-8.024e-001,+1.718e-001)\n  (-4.714e-001,-2.868e-001)\n  (-8.408e-001,-7.916e-002)\nZ:\n  (+1.268e-003,+0.000e+000)\n  (+1.933e-001,-8.132e-019)\n  (+5.850e-001,+0.000e+000)\n  (+3.503e-001,-1.789e-018)\n  (+8.228e-001,+0.000e+000)\n  (+1.741e-001,+9.595e-018)\n  (+7.105e-001,+0.000e+000)\n  (+3.040e-001,-6.993e-018)\n\u8bf7\u6309\u4efb\u610f\u952e\u7ee7\u7eed. . .<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
fft \/ ifft \u7528\u9014\uff1afft \/ ifft\u51fd\u6570\u7528\u4e8e\u4e00\u7ef4\u5feb\u901f\u5085\u91cc\u53f6\u53d8\u6362\/\u5feb\u901f\u5085\u91cc\u53f6\u9006\u53d8\u6362\u3002\u8be5\u51fd\u6570\u91cd\u8f7d\u6709cx […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-36","post","type-post","status-publish","format-standard","hentry","category-algorithm"],"_links":{"self":[{"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/posts\/36","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=36"}],"version-history":[{"count":1,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/posts\/36\/revisions"}],"predecessor-version":[{"id":37,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=\/wp\/v2\/posts\/36\/revisions\/37"}],"wp:attachment":[{"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=36"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=36"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chaixiangyu.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=36"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}