octave:2> A=rand(4) A = 0.486767 0.762796 0.747325 0.019163 0.745053 0.209979 0.848402 0.188778 0.490122 0.554519 0.129443 0.128222 0.259436 0.300709 0.353963 0.695869 octave:3> b=rand(4,1) b = 0.356326 0.560230 0.060687 0.695767 octave:4> x=A\b x = -0.148803 -0.085989 0.641851 0.766003 octave:5> A*x ans = 0.356326 0.560230 0.060687 0.695767 octave:6> b b = 0.356326 0.560230 0.060687 0.695767 octave:7> norm(A*x-b) ans = 1.4221e-16 octave:8> x=49/49 x = 1 octave:9> y=(1/49)*49 y = 1.0000 octave:10> format long e octave:11> y=(1/49)*49 y = 1.00000000000000e-00 octave:12> y==1 ans = 0.00000000000000e+00 octave:13> x==1 ans = 1.00000000000000e+00 octave:14> abs(y-1) ans = 1.11022302462516e-16 octave:15> A A = Columns 1 through 3: 4.86766902694725e-01 7.62795664883696e-01 7.47325468656905e-01 7.45053262678666e-01 2.09979116704892e-01 8.48402064258132e-01 4.90121975116431e-01 5.54519367871767e-01 1.29443220079375e-01 2.59436385632634e-01 3.00709316762376e-01 3.53962996660267e-01 Column 4: 1.91633276272952e-02 1.88778070976837e-01 1.28221761226010e-01 6.95869090002766e-01 octave:16> format short octave:17> format short octave:18> A A = 0.486767 0.762796 0.747325 0.019163 0.745053 0.209979 0.848402 0.188778 0.490122 0.554519 0.129443 0.128222 0.259436 0.300709 0.353963 0.695869 octave:19> B=rand(4) B = 0.140061 0.503196 0.177782 0.443711 0.844300 0.187181 0.801216 0.927123 0.262106 0.421326 0.063937 0.069704 0.817163 0.040615 0.733658 0.251686 octave:20> A\B ans = 0.8387168 0.2719905 0.4057925 0.5032325 -0.5414100 0.6026068 -0.5710741 -0.4990047 0.1678350 -0.1125999 0.5339560 0.7754092 1.0102028 -0.2461710 0.8781929 -0.0047164 octave:21> A=[1 2 3;4 5 6;7 8 9] A = 1 2 3 4 5 6 7 8 9 octave:22> det(A) ans = 0 octave:23> A(1:2,:) ans = 1 2 3 4 5 6 octave:24> 1:2 ans = 1 2 octave:25> [1:2+ > octave:25> [1:2] ans = 1 2 octave:26> [2 1] ans = 2 1 octave:27> A([2 1],:) ans = 4 5 6 1 2 3 octave:28> A([1 3 2],:) ans = 1 2 3 7 8 9 4 5 6 octave:29> A([2 1 3],:) ans = 4 5 6 1 2 3 7 8 9 octave:30> A=[1 2 3 4;5 6 7 8;9 10 11 12; 13 14 15 16] A = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 octave:31> A([1 2 4],:) ans = 1 2 3 4 5 6 7 8 13 14 15 16 octave:32> B B = 0.140061 0.503196 0.177782 0.443711 0.844300 0.187181 0.801216 0.927123 0.262106 0.421326 0.063937 0.069704 0.817163 0.040615 0.733658 0.251686 octave:33> A A = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 octave:34> [A,B] ans = Columns 1 through 6: 1.000000 2.000000 3.000000 4.000000 0.140061 0.503196 5.000000 6.000000 7.000000 8.000000 0.844300 0.187181 9.000000 10.000000 11.000000 12.000000 0.262106 0.421326 13.000000 14.000000 15.000000 16.000000 0.817163 0.040615 Columns 7 and 8: 0.177782 0.443711 0.801216 0.927123 0.063937 0.069704 0.733658 0.251686 octave:35> [A;B] ans = 1.000000 2.000000 3.000000 4.000000 5.000000 6.000000 7.000000 8.000000 9.000000 10.000000 11.000000 12.000000 13.000000 14.000000 15.000000 16.000000 0.140061 0.503196 0.177782 0.443711 0.844300 0.187181 0.801216 0.927123 0.262106 0.421326 0.063937 0.069704 0.817163 0.040615 0.733658 0.251686 octave:36> A A = 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 octave:37> max(A(:,2)) ans = 14 octave:38> [m,i]=max(A(:,2)) m = 14 i = 4 octave:39> [m,i]=max(A(2:4,2)) m = 14 i = 3 octave:40> A(2:4,2) ans = 6 10 14 octave:41> diary off