Matlab学习笔记04

书籍：Matlab实用教程
工具：Matlab2021a

电脑信息：Intel® Xeon® CPU E5-2603 v3 @ 1.60GHz

系统类型：64位操作系统，基于X64的处理器 windows10 专业版

第2章 MATLAB数值计算
2.2.5 多维数组

a(:,:,2)=[1 2;3 4] a = ans(:,:,1) = 0 0 0 0 ans(:,:,2) = 1 2 3 4 b=[1 1;2 2] b = 1 1 2 2 b(:,:,1) ans = 1 1 2 2 b(:,:,2)=5 b = ans(:,:,1) = 1 1 2 2 ans(:,:,2) = 5 5 5 5 rand(2,4,3) ans = ans(:,:,1) = 0.7545 0.9408 0.3400 0.5408 0.9729 0.1218 0.5788 0.8096 ans(:,:,2) = 0.815615 0.130754 0.712230 0.506144 0.671953 0.626479 0.351647 0.050380 ans(:,:,3) = 0.846819 0.642756 0.888265 0.035262 0.926687 0.579137 0.695622 0.339919 ones(2,4,3) ans = ans(:,:,1) = 1 1 1 1 1 1 1 1 ans(:,:,2) = 1 1 1 1 1 1 1 1 ans(:,:,3) = 1 1 1 1 1 1 1 1 a=[1 2;3 4] b=[1 1;2 2] c=cat(2,a,b) d=cat(3,a,b) e=repmat(a,[2 2 2]) f=reshape(c,[2 2 2]) a = 1 2 3 4 b = 1 1 2 2 c = 1 2 1 1 3 4 2 2 d = ans(:,:,1) = 1 2 3 4 ans(:,:,2) = 1 1 2 2 e = ans(:,:,1) = 1 2 1 2 3 4 3 4 1 2 1 2 3 4 3 4 ans(:,:,2) = 1 2 1 2 3 4 3 4 1 2 1 2 3 4 3 4 f = ans(:,:,1) = 1 2 3 4 ans(:,:,2) = 1 1 2 2 a=[1 2;3 4;5 6] ndims(a) size(a) size(a,2) length(a) a = 1 2 3 4 5 6 ans = 2 ans = 3 2 ans = 2 ans = 3

2.3 稀疏矩阵

a=eye(3) a(4,:)=[-5 - -3] b=sparse(a) c=sparse([1 4 2 4 3 4],[1 1 2 2 3 3],[1 -5 1 -2 1 -3]) full(b) a = Diagonal Matrix 1 0 0 0 1 0 0 0 1 a = 1 0 0 0 1 0 0 0 1 -2 -2 -2 b = Compressed Column Sparse (rows = 4, cols = 3, nnz = 6 [50%]) (1, 1) -> 1 (4, 1) -> -2 (2, 2) -> 1 (4, 2) -> -2 (3, 3) -> 1 (4, 3) -> -2 c = Compressed Column Sparse (rows = 4, cols = 3, nnz = 6 [50%]) (1, 1) -> 1 (4, 1) -> -5 (2, 2) -> 1 (4, 2) -> -2 (3, 3) -> 1 (4, 3) -> -3 ans = 1 0 0 0 1 0 0 0 1 -2 -2 -2 D=[3 2 9;2 4 9;1 1 4] d=[0 1 2] s=spdiags(D,d,4,3) full(s) D = 3 2 9 2 4 9 1 1 4 d = 0 1 2 s = Compressed Column Sparse (rows = 4, cols = 3, nnz = 6 [50%]) (1, 1) -> 3 (1, 2) -> 4 (2, 2) -> 2 (1, 3) -> 4 (2, 3) -> 1 (3, 3) -> 1 ans = 3 4 4 0 2 1 0 0 1 0 0 0 X=[1 1 1;4 1 -5;2 2 1;4 2 -2;3 3 1;4 3 -3] b=spconvert(X) nnz(b) nonzeros(b) nzmax(b) spy(b) X = 1 1 1 4 1 -5 2 2 1 4 2 -2 3 3 1 4 3 -3 b = Compressed Column Sparse (rows = 4, cols = 3, nnz = 6 [50%]) (1, 1) -> 1 (4, 1) -> -5 (2, 2) -> 1 (4, 2) -> -2 (3, 3) -> 1 (4, 3) -> -3 ans = 6 ans = 1 -5 1 -2 1 -3 ans = 6