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

复制代码

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

复制代码

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