三、结构化程式与自定义函数

1、Script writing
2、Structured programming
3、User-defined function

1、Script writing

1.1 MATLAB Script

• A file containing a series of MATLAB commands
• Pretty much like a C/C++program
• Scripts need to be saved to a <file>.m file before they can be run

image.png image.png

for i=1:10
    x=linspace(0,10,101);
    plot(x,sin(x+i));
    print(gcf,'-deps', strcat('plot',num2str(i),'.ps'));
end

结果：

image.png

debug:

image.png
image.png

1.2 Script Flow

• Typically scripts run from the first line to the last

  
  image.png
• Structured programming techniques(subroutine,loop, condition,etc)are applied to make the program looks neat

Flow Control：

image.png

Relational(Logical)Operators：

image.png

• if elseif else

if condition1  # 条件
    statement1  # 动作
elseif condition2
    statement2
else
    statement3
end

例子：

a = 3;
if rem(a,2) == 0  # rem是求余数的函数
    disp('a is even')  # even偶数
else
    disp('a is odd')  # odd奇数
end

• "elseif" and "else" are optional

• switch

switch expression
case value1    
    statement1
case value2
    statement2

otherwise
    statement
end

例如：

input_num = 1;
switch input_num
    case -1
        disp('negative 1');
    case 0
        disp('zero');
    case 1
        disp('positive 1');
    otherwise
        disp('other value');
end

结果：

>> M03
positive 1

• while

while expression
      statement
end

例子：

n = 1;
while prod(1:n) < 1e100     % prod()各元素相乘   e100是10的100次方
    n = n + 1;
end
n

结果：

>> M03
n =
    70

Exercise

Use while loop to calculate the summation of the series 1+2+3+...+999

n = 1
a=0
while n<1000
    a = a + n
    n = n+1
end
a

结果：

a =
      499500