Matlab 基础与应用

• ans
• pi
• eps
• Inf
• NaN
• realmax
• disp

• vec1 = [1,2,3];  %产生一个行向量
  vec2 = [1,2,3]'; %产生一个列向量
  vec3 = [1:0.5:3] %产生一个第一个元素为1
                   %最后一个元素不超过3
                   %步长为0.5的等距行向量
   
  mat1 = [1,2,3;3,4,5]  % 2x3
  mat2 = zeros(3,4)     % 3x4 O
  mat3 = ones(3,4)      % 3x4 1
  mat4 = eye(4);        % 4阶单位矩阵
   
  m12 = mat1(2,3)       % 矩阵第二行第三列的元素
   
   
  

• 点运算 

• x = [1,2,3];
  x = x.^2;    %[1,4,9]
  y = [2,3,4];
  y = x.*y;    %[2,12,36]
  

• x = [0:0.1:2*pi];
  y = sin(x). *cos(x.^2);
  plot(x,y,"r-")
  

• x = randperm(4);    %产生1-4的随机排列
  y = randperm(4);    
   
  c0 = (x>y);         %一种可能的结果(1,1,0,0)
  c1 = ~(x>y);        %取反
  c2 = (x>2) & (x<4); %与运算
  c3 = (x>2) | (x<4); %或运算
   
  a = 1;
  b = sqrt(2);
  a==1 && b==1;
  a==1 || b==1;
  

• x = 1+2i'
  z = complex(2,3);
  real(z);   %2
  imag(z);   %3
  angle(z);  %辐角运算
  

•  for-end
•  while-end

• if-elseif-else-end
• swithc-case-otherwise-end

  • result = 78;
    switch(result)
        case 52
            disp("result is 52.")
        case {52,78}
            disp("result is 52 or 78")
        otherwise
            disp("no result!")
    end
    

• A = [1,2,3;4,5,6];
  B = A/2;
   
  C = A+B;
  D = A*B';
  E = diag(A);    %取对角元素，生成列向量
  r1 = A(1,:)     %第一行
  c2 = A(:,2)     %第二列
  A(1,[1,3])      %第一行 第一列 第三列
  A([1,2],[1,3])  %[1,1],[1,3],[2,1],[2,3]
  d = r1(2:end)   %取2-最后一个元素
  

• A = rand(10000);
  tic;
  B=A(find(A>0.3 & A<0.7));
  toc;
  tic;
  C = A((A>0.3&A<0.7));
  toc;
  

• n = 3000;
  tic;
  for k = 1:n
      a(k)=1;
  end
  b = zeros(1,n,"double")
  toc;
  tic;
  for k=1:n
      b(k) = 1;
  end
  toc;
   
   
   
  历时 0.012460 秒。
  历时 0.000736 秒。
  

• %表示pi
  PI = 4*atan(1)
  

• 创建

  • clc;
    D = [1,2,3;2,3,4;3,4,5];
    Dd(:,:,1)=D;
    Dd(:,:,2)=2*D;
    Dd(:,:,3)=3*D;
    

• 高维数组的访问

  • sum(Dd,3)
     
    ans =
     
         6    12    18
        12    18    24
        18    24    30
    

• A = [[0,0,0],
      [1,0,2],
      [1,0,2],
      [1,0,2]];
  A(:,~sum(abs(A),1))=[];
  A(~sum(abs(A),2),:)=[];
  disp(A)
   
       1     2
       1     2
       1     2
  

function [rtn1,rtn2] = functionName(x,y)
rtn1 = x+y;
rtn2 = x*y;
end 
 
 
%保存在同一目录下,
%调用
 
x = 1;
y = 3;
[rtn1,rtn2] = functionName(x,y);

• %匿名函数语法
   
  fhandle = @(arglist1)@(arglist2)  expr
   
  f = @(x)  x.^2;
  g = @(a,b)@(x)  a*x+b;
  x = linspace(0,1,10);
  plot(x,f(x));
  g1 = g(1,2)
  plot(x,g1(x))
  

•  

  f = @(a) @(x) exp(x)+x^a+x^(sqrt(x))-100;
  g = @(a) fzero(f(a),4);
  aa = 0:0.01:2;
  ff = arrayfun(g,aa);
  plot(aa,ff,"r.-")
  

syms x
f = (x+tan(x))^(sin(x));
c = diff(f,3);
funstr = ['@(x)' vectorize(c)];
f3 = eval(funstr);
x = linspace(0,1,100);
plot(x,f3(x),'linewidth',2);