how to make a sub matrix from specific indices

sizeA = [1400 1400];
indices = [312
323
673
876
1031
1326
1344
1354
1359
1384];
[r, c] = ind2sub(sizeA, indices);
nummat = size(r,1);
mats = cell(nummat,1);
for K = 1 : nummat
    mats{K} = A(r(K):r(K)+9, c(K):c(K)+9);
end

Yes, it would be possible to vectorize this a bit, but the code would be notably more difficult to understand.

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VBBV 2023-4-14

编辑：VBBV 2023-4-14

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Both ind2sub & sub2ind are able to produce the 10 x10 matrix format, but which one is correct here is confusing for me,

sizeA = [1400 1400];
A = randn(1400);
indices = [312
323
673
876
1031
1326
1344
1354
1359
1384];
[r c] = ind2sub(sizeA, indices);
nummat = size(r,1);
mats = cell(nummat,1);
for K = 1 : nummat
    mats{K} = A(r(K):r(K)+9, c(K):c(K)+9);
end
mats{:}
ans = 10×10
    1.2274    0.3295    0.7968    1.4923   -0.7608    0.7907   -0.5803    0.2214    1.2191   -0.2977
    0.4435   -1.4633   -0.7854    1.7629   -1.2268    0.8160   -1.0832   -0.9987   -0.4603    0.6937
   -0.9401   -0.6759    0.8486   -1.0199    2.0416   -0.3673   -0.3748    0.1962   -0.6763   -2.5935
   -0.5716    0.4462    1.7819   -0.1581    1.6739    0.0326    0.4167    0.5241   -1.1618    0.8784
   -0.8986   -0.6070    0.0067    1.1046    1.2513   -1.4109   -0.9435    0.8504    1.7319    1.0161
   -0.2454   -2.1883   -0.1573    1.0006   -0.7103    0.1212   -0.4622   -0.1738    0.3173   -0.1019
    0.7547   -0.5365   -0.9112   -2.0777    0.3595   -0.6276   -0.2749   -0.3126    1.2341    0.4672
    0.1448   -0.5764   -0.2750    0.2195    1.0517    0.3727   -0.3154    0.7365    0.2040    0.1246
    0.5426   -0.1619    0.0019    2.6920    1.1146    0.1145   -0.0051    0.9233    0.4249    1.4796
   -0.6364    0.6818   -1.7166   -1.4217   -1.6261    1.8180   -1.3637    0.8519   -0.3774   -0.7804
ans = 10×10
    0.6697   -0.2216    0.6877   -1.8931   -0.0014   -0.6697    0.0405   -0.1257   -1.5222   -0.4424
   -0.4472   -0.6073    0.4856   -0.2113   -0.0960    0.9896    0.3959    0.1211   -0.7276    0.2936
   -0.2850    0.6803    0.3817    1.4337   -1.0523   -0.0551    1.5178    0.9039    1.3457    0.9360
   -0.8927   -0.5396   -0.3796   -0.7903   -0.7854   -1.6147    0.3620    0.6523   -1.1203    0.2483
   -0.7449   -0.9152   -0.7908   -0.0733    0.5327   -1.7781    1.4260   -0.2516   -1.0976    0.4227
   -1.2642    0.1351    0.0347    0.0540   -0.2795    0.6524   -1.9098    1.3335   -1.2926   -0.9181
    0.9319   -1.0401   -0.7477   -1.7887   -1.5969    0.5209    0.4045    1.5619   -0.1162    1.7773
    0.0869   -0.5220    1.1894   -1.3465    1.5531    0.0609    0.7463    1.0551   -0.0238   -0.1360
   -1.2583    0.6302    0.2016    0.3634    0.2360   -0.6430    0.9249    0.7618    0.0457   -0.7809
    1.3842    0.3534   -0.0488    1.4713   -0.4480   -1.7879    0.3722    0.8602   -0.3932    0.2565
ans = 10×10
   -2.4064    0.5570   -0.8339   -2.4067    1.3686    0.6052    1.7021   -0.0917    0.7401   -0.5899
    1.7309    0.0620    1.1621   -0.6396    0.0083   -0.0413   -1.4599    1.4072   -0.9151   -0.0624
   -2.1788   -0.1313    0.4904    0.4537   -0.8098    1.0716   -0.6214   -1.2674    1.1373    0.3682
    2.3037    0.1686    0.6020    0.7145   -0.5152   -1.0540    0.6063    0.1481    0.6786   -0.7383
    1.0603    1.0721    0.5414   -0.2556   -1.2218   -0.2641   -1.7006   -0.9535    1.1841    1.3660
    1.1520    0.7860   -0.9208   -0.3916   -0.1032    0.3456    2.0979   -0.1338   -0.5450   -0.3687
   -1.6381    0.6963   -1.3700    1.1938    0.3811   -0.5439    1.5586    0.3399   -0.3875   -0.5935
   -0.4899   -1.1105   -0.7849    0.5704    0.8833    0.9133    0.8279    0.8836    0.6648    2.0661
    0.8146    0.1991   -0.1595   -0.6342    0.1025    0.6582   -0.6770   -1.0532    0.3205   -1.6026
   -1.1088   -0.1052    0.8062   -0.1685   -0.9004    0.0265    0.0214   -1.6802   -0.6561   -1.5523
ans = 10×10
    1.1268    0.0370    1.2579   -0.6739   -0.4390   -0.4109    0.7583   -0.8408    2.2990   -0.8014
    0.1990    0.8289    1.8590   -0.8605   -0.3906    1.5655    1.2351   -0.6535   -1.1849   -0.3863
   -0.7625   -2.2754    0.7528    0.3255   -0.8675    0.4560    2.4472    0.8346    0.6872   -0.4408
   -0.3979    0.8189   -0.6469   -0.2538   -0.7524   -1.1820    0.4280    1.4433    0.2509   -1.2179
   -0.5213   -0.9014   -0.8947    0.4506    0.6618    1.4883    0.0988    0.8976    1.0143   -0.3166
    1.2459    0.5731   -0.0862    0.0879   -0.1629    0.0623    1.2049    0.1768   -0.0708   -1.4698
   -0.7387   -1.1931    0.7336   -0.9635    0.7394   -1.2931    0.5884    1.0487   -1.6886    0.7649
   -0.0832   -0.1566    1.1809    0.9180    0.2742   -0.9146   -0.6467    0.1735    1.1813   -0.9604
   -0.1030   -1.3454   -0.9303   -0.5204    2.0201    1.6035   -0.4046    0.0663    0.4674   -1.2442
    0.2572   -0.5886    1.2753   -0.7095   -1.3927   -1.5557   -0.4019    2.3746   -1.6129    0.8868
ans = 10×10
    0.9847   -0.4020   -0.5251    0.1701   -0.6140   -0.6884    0.6534   -0.3032    0.3091   -0.3692
    0.9861   -0.4543    1.5570   -0.2683    0.7104    0.3965    0.9716   -0.1630   -0.5840    0.0969
    0.7748   -0.6726    1.0529   -2.1886    0.3496    0.2964   -1.0824    0.0658    0.2957    0.8040
   -0.3948    0.1086    0.1299   -1.5286   -0.9352    0.8854   -0.2151   -0.9710   -0.0098   -0.3886
   -0.9170   -0.4063   -1.2175    0.2642    0.3906    0.5182    0.9190   -0.1160    0.5534   -2.1486
    0.0223   -1.6013    0.8343   -0.9097    1.8630    0.2969    0.5699   -0.4728   -1.7668    0.2987
   -0.5719   -0.2976    0.1616   -1.2727    0.6519   -0.3377   -0.0481    0.1742   -0.4020    1.5383
    1.9145   -0.2494    0.5216   -1.5958   -0.5605    0.1725    0.2519    1.8173   -0.7086   -0.4622
   -0.4151    1.3074   -0.9092   -1.5118   -0.0560   -1.3397    2.1519    0.3999    1.3701   -0.5088
    0.1468   -0.1830   -0.3500   -1.2348   -0.0941   -0.1012    1.2819    1.4033   -1.1342   -0.0837
ans = 10×10
    0.0933    1.5828    0.4261   -0.4075    1.7207    0.3468    0.7990    0.5301   -2.3321   -0.2226
   -0.1458    1.0198   -1.3263    0.4327   -0.2883    0.1084   -0.0221   -0.5067    0.7344   -0.3785
    0.6271   -0.2777   -0.2144    1.5244    0.0726   -0.9391   -0.5420    1.5376   -2.1879    1.7058
    1.2357    2.7229    0.0155   -0.4603    0.5415   -0.1820    0.1462    0.0159    1.7782   -0.6156
   -1.6198   -0.6055   -0.3607    0.5433   -0.0195   -1.8119    0.2418    1.4614   -1.6690    0.2379
   -1.3812   -1.1528   -0.7278    0.4328    1.0143    1.0823   -0.6154    1.0609    1.2193   -0.1190
    0.0039   -0.9788   -0.0482    0.5554    1.0455    0.3008   -0.4074   -0.6076    0.8555   -0.4619
    0.5751    0.4971   -0.5637   -1.4416    0.3489   -0.2736   -0.3581    2.1733   -1.0961   -1.3528
    1.7314   -1.7163   -0.7950    0.8097    0.2180   -1.3015    1.1040   -0.4973    0.5934   -0.9828
    1.0615    1.2497   -1.7331    0.1935    1.8003    0.3016   -0.9228    0.6502    1.1792    1.5103
ans = 10×10
   -0.4503    0.8373   -0.8358    1.6776    1.0439   -1.4601   -0.4207    0.6244   -0.5346    0.3198
    0.9552   -0.1955   -1.9583   -0.4792    0.0437   -0.0828   -0.5921    1.1775   -0.1669    0.2423
    0.5675   -0.8013    1.5307   -1.1743   -0.1577   -0.2642    0.0203   -1.2842    0.9979   -0.4941
   -0.4357    0.3852    0.9015    1.1771    0.1913    1.0853   -1.3117    1.2533    0.0945    1.4830
    0.1810   -1.7190   -1.4033   -0.5826   -1.1408   -0.9292   -0.5815   -0.1439   -0.3964    0.4006
    0.8684    0.7353   -1.3325    1.5264   -1.1969   -0.5514   -1.0830    0.1895   -2.2601    0.8543
    1.9686    2.0115    0.2306   -1.0766    1.7776   -0.3819    1.4037    0.2358    0.0671    0.4554
   -1.2876    0.4543   -2.1239   -0.4798    1.3068   -0.6482   -0.0127   -1.4443   -0.4105    0.8932
    0.4975   -0.5648    1.7621   -0.3012   -0.8388    0.1537    0.3617    1.5525    0.0675   -1.4487
   -0.4951    1.9292    1.7286   -0.1753   -1.1269   -0.9260    0.9436    0.5801   -1.1331    0.4536
ans = 10×10
    1.1286   -1.3361   -1.4970    0.6643   -0.7034    0.5047   -0.5886   -0.1161    0.4318    1.5564
   -0.5444    0.0786    0.1863   -1.0993   -1.7784    0.2960   -0.6002   -0.6993   -0.4482    1.1978
    1.1724   -0.6675    0.9070   -1.5070   -0.0034   -0.5917    1.1190   -0.3524   -0.5115   -1.9743
    0.6043   -0.7524    0.2611    0.2953   -0.2356    1.1350    2.1098    0.0302   -0.0072    0.1504
    0.3063    0.3137   -0.5007   -0.5035   -0.2251   -0.4456    0.1703    0.0302   -2.4383   -0.5960
   -0.3456    2.1602   -0.8945    0.6599    0.7097    0.0978    2.0203   -1.0533    0.7168   -0.3909
   -0.4985    2.0481    0.8436    0.1718    0.5416    1.7352    0.8161    1.0455   -0.0929    1.2690
    0.4820    0.0320    1.0301   -0.4336    0.5284    0.1875    2.2568   -0.4538   -0.1784    0.2202
   -1.3458    0.5211    2.6368    0.6873   -1.4840    0.5279   -0.8495   -0.7011    1.2811    1.4801
    0.7558    1.1309    0.3442    0.3185    1.8050    2.3447   -0.5398    1.3449   -0.8441    0.9285
ans = 10×10
   -0.3456    2.1602   -0.8945    0.6599    0.7097    0.0978    2.0203   -1.0533    0.7168   -0.3909
   -0.4985    2.0481    0.8436    0.1718    0.5416    1.7352    0.8161    1.0455   -0.0929    1.2690
    0.4820    0.0320    1.0301   -0.4336    0.5284    0.1875    2.2568   -0.4538   -0.1784    0.2202
   -1.3458    0.5211    2.6368    0.6873   -1.4840    0.5279   -0.8495   -0.7011    1.2811    1.4801
    0.7558    1.1309    0.3442    0.3185    1.8050    2.3447   -0.5398    1.3449   -0.8441    0.9285
   -0.3737   -0.7873    1.6613    0.4257   -0.7976   -0.0925   -1.0963    0.4607    2.2001   -0.6749
    1.1886   -0.6613    1.1697    0.3777   -0.6765    0.5386   -0.3835    0.0877   -0.4095    1.2290
   -0.8211    0.8848    0.7490   -0.5707    0.9414   -1.5440   -0.8125   -0.5192    0.8658   -0.8438
    1.6599    0.7769    0.4541   -0.1691    0.7683   -1.9636    0.9507    0.8829   -1.5058    0.1840
   -2.1856    0.2031   -0.3591    0.3669   -0.6781    0.5134   -0.5405   -0.4923   -1.0761    0.7079
ans = 10×10
   -1.3066    0.1792   -0.3632   -0.2916    1.6796    1.3848    0.9249   -1.1241    0.8276   -0.6299
    0.4465   -1.0432   -2.0024   -0.3961    0.2425   -1.3310    0.9709    0.6972   -1.3396   -1.4757
    0.7585    0.0243    0.7183    1.3754   -0.7643    0.8189    2.5932   -0.3269    0.4465    0.9266
    0.7364    0.4367    0.3985   -0.2891   -1.4749   -2.3235   -0.2126    2.1990   -0.1747   -0.4467
    0.0126    0.3232    1.0698    0.5077   -1.4442    2.2230    0.4276   -1.5945    0.1920   -2.7698
    0.8809   -0.1422    1.2161    1.8356    1.0401   -1.0258   -0.2862   -0.3394    0.2612    2.0778
   -0.0869   -1.2442   -0.4470   -1.1189   -1.0614   -0.6622    0.9346   -1.3191   -0.1541   -0.4887
   -1.7913   -0.5962    0.2035   -0.1535    1.2930    0.4868    1.2997   -1.0880   -0.0098    0.4224
    0.9853    0.5005   -0.1731    0.9143   -0.8004   -1.7848   -0.9680   -1.8426    0.2232    1.3747
   -1.1119    1.4142   -1.0316   -0.4480   -0.2625    0.1601   -1.4253   -1.2456    0.6185    0.7708