假设我有两个m×n矩阵A和B。 B是零\一二进制矩阵。对于(i,j)中包含1的每个单元B，我想进行以下计算：
(A(i,j)sign(A(i+1,j))-A(i+1,j)sign(A(i,j)))/(sign(A(i+1,j))-sign(A(i,j)))
答案 0 :(得分：1)
您可以直接使用B来索引矩阵A中要进行计算的位置。更难的部分来自于您需要在i+1处获取值。
如果你在B的最后一行中有1个值，那么你去下面一行的值可能会有问题，我将在下面假设你没有。如果你这样做，只需处理这个案例并将0＆＃39;放在B的最后一行。
% Get the indexes from your matrix B :
Indexes=find(B(:));
% With how indexing works in MATLAB, you can fetch the value in the row below the fetched index by just adding 1 to the indexes :
% Note : This is where it will mess up if you have 1's in the last row of `B`
Indexes_Next=Indexes+1;
% Do your calculation and fill them in a matrix `C`, using the indexes :
C=zeros(size(A));
C(Indexes)=A(Indexes).*sign(A(Indexes_Next))-A(Indexes_Next).*sign(A(Indexes))./sign(A(Indexes_Next))-sign(A(Indexes));
m=20;
n=10;
B=randi(2,m,n)-1;
B(end,:)=0;
B =
1 1 1 0 1 0 0 0 1 1
1 1 1 0 0 0 1 1 1 0
1 0 1 0 1 0 0 1 1 1
1 0 1 1 1 0 0 1 1 0
0 1 0 0 1 1 0 0 0 0
1 1 0 1 0 1 0 1 1 0
1 1 1 1 1 0 0 0 1 1
1 0 1 1 0 0 1 0 1 0
1 0 0 0 1 1 0 0 0 0
1 0 0 0 0 1 1 0 1 1
1 0 0 1 1 1 0 0 1 1
1 0 0 1 0 1 1 0 0 0
0 0 0 0 0 1 0 0 1 1
1 0 1 0 0 0 0 1 0 0
0 1 1 1 1 0 1 0 0 1
1 0 1 1 1 0 0 0 0 1
1 0 1 0 0 1 1 1 1 0
0 0 0 0 0 1 0 1 1 0
0 1 0 1 1 0 1 1 0 0
0 0 0 0 0 0 0 0 0 0
A=randn(m,n);
A =
Columns 1 through 6:
-1.7288795 -0.5695908 0.4039973 0.4178222 1.9367721 -0.6211859
-0.4945766 -0.2536017 1.0269974 0.5980587 0.1747083 0.8528545
0.9100027 0.9414117 1.6132723 0.2620914 -1.1753700 0.1701842
-0.5094579 -1.5272232 -0.0270926 1.1561264 -0.8968151 0.5069460
-0.4602732 -0.2735907 -0.0827892 0.1235966 0.2566247 -0.6536810
0.0021322 0.2238454 -1.9115733 1.0635302 -0.9725437 0.9375332
1.1415043 0.7147173 1.1052473 -1.0797606 -1.0508984 -0.8286737
-1.1394488 -0.9882800 0.8274943 0.5247194 0.1164014 1.6475021
-0.6300175 -0.2726597 1.9213140 -0.2248069 0.8301544 1.2854954
0.9846066 -0.0560177 -0.1916319 0.8563492 0.1493325 -1.1080141
0.8041186 0.3818663 -0.6250196 0.4691516 1.6304691 1.9712590
0.3986143 0.2072083 0.5478786 0.8156810 0.7733391 0.1741200
2.1892863 -0.6791961 -0.5672075 -1.2172510 -2.1611237 0.2908826
-0.0317070 0.7387466 -0.8868863 -1.6897724 0.0445329 -0.7162208
0.7670334 0.1991324 -1.8576145 -0.9314224 0.3317805 2.3690729
-0.2091770 2.1657798 -1.0850389 -0.5931122 -1.6465039 -1.8521626
-0.7298015 0.5714788 -1.9456336 2.5631989 0.8980204 0.7283266
0.0126946 -2.0152983 0.0837190 0.0824572 -1.9949677 -0.7532233
0.6209000 -1.5505561 -0.0273443 -0.0888351 0.3024363 0.0104319
0.1721166 -0.9743276 2.1976957 -0.5196333 0.4917723 0.5235348
Columns 7 through 10:
-1.3386919 1.5511076 -0.0823747 0.6598207
0.1000738 1.3927819 1.2658383 0.3986191
-0.3424243 -1.3382283 -0.9360141 1.3003693
-0.6647429 -0.4520907 -0.6012909 0.7016295
-1.2671007 1.0972997 -0.6613468 0.2677242
-0.7083392 0.8622831 1.1582403 0.7597853
0.3218546 1.7128733 0.6578481 -1.7975630
-0.1816331 0.1582915 0.0125391 -1.6381652
1.1860973 -0.2897986 0.9418221 0.5233429
0.9335806 0.2088674 -1.1177073 -0.3280461
0.8333193 0.7273941 -0.6683300 -0.6137806
0.0360114 -0.3457279 -0.9115280 -0.6171204
-1.2861883 -0.7169084 -0.4313750 -0.4534017
-0.3267513 -0.3327733 1.0649930 0.9503430
0.3513518 0.7668540 0.8704655 0.3367261
0.6942558 -0.0811757 -0.0930538 0.4074495
0.0882976 -0.2911365 -3.0432331 -0.3264093
0.4319805 -0.3641444 0.3984263 -0.0481398
0.8404379 -0.4123483 -0.0465423 -0.1831455
-0.8230964 0.3130749 0.6854873 -0.2411392
Output :
--------
C
C =
Columns 1 through 8:
3.22346 1.82319 -1.62300 0.00000 0.76206 0.00000 0.00000 0.00000
1.41543 1.68781 -1.58627 0.00000 0.00000 0.00000 -1.44250 -3.73101
-2.41946 0.00000 -2.64036 0.00000 3.07219 0.00000 0.00000 2.79032
1.96973 0.00000 1.10988 0.03253 0.35981 0.00000 0.00000 1.64521
0.00000 0.95025 0.00000 0.00000 -2.22917 1.28385 0.00000 0.00000
-2.13937 -1.49087 0.00000 -3.14329 0.00000 -2.76621 0.00000 -1.85059
-3.28095 -2.70300 -0.72225 0.44496 0.06550 0.00000 0.00000 0.00000
2.76947 0.00000 -2.09382 -1.74953 0.00000 0.00000 2.00446 0.00000
1.35459 0.00000 0.00000 0.00000 -0.31918 -3.39351 0.00000 0.00000
-0.81951 0.00000 0.00000 0.00000 0.00000 1.86324 -0.89974 0.00000
-0.59450 0.00000 0.00000 -1.34653 -0.14287 0.79714 0.00000 0.00000
-2.79067 0.00000 0.00000 -3.03293 0.00000 -1.11676 -2.32220 0.00000
0.00000 0.00000 0.00000 0.00000 0.00000 -2.00710 0.00000 0.00000
1.73533 0.00000 3.74450 0.00000 0.00000 0.00000 0.00000 1.43408
0.00000 -2.96665 3.94265 2.52453 -2.97828 0.00000 -1.34290 0.00000
1.93898 0.00000 4.03067 2.97009 0.25152 0.00000 0.00000 0.00000
0.28289 0.00000 -0.86191 0.00000 0.00000 -2.48155 -1.34368 1.65528
0.00000 0.00000 0.00000 0.00000 0.00000 0.25721 0.00000 1.77649
0.00000 3.52488 0.00000 1.60847 -1.18934 0.00000 -2.66353 0.90073
0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
Columns 9 and 10:
2.18346 -0.73880
-3.20185 0.00000
2.53731 -0.40126
2.26264 0.00000
0.00000 0.00000
-0.49961 0.00000
-0.35469 4.43573
-1.92928 0.00000
0.00000 0.00000
2.78604 1.94183
2.57986 2.23090
0.00000 0.00000
1.63362 1.49694
0.00000 0.00000
0.00000 -1.07072
0.00000 -1.73386
-1.64481 0.00000
-1.44497 0.00000
0.00000 0.00000
0.00000 0.00000