octave函数

　　在octave中有很多的函数应用，例如：命令type magic查看magic函数的源码

magic is the user-defined function defined from: /usr/share/octave/6.4.0/m/special-matrix/magic.m

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## along with Octave; see the file COPYING.  If not, see
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########################################################################

## -*- texinfo -*-
## @deftypefn {} {} magic (@var{n})
##
## Create an @var{n}-by-@var{n} magic square.
##
## A magic square is an arrangement of the integers @code{1:n^2} such that the
## row sums, column sums, and diagonal sums are all equal to the same value.
##
## Note: @var{n} must be a scalar greater than or equal to 3.  If you supply
## @var{n} less than 3, magic returns either a nonmagic square, or else the
## degenerate magic squares 1 and [].
## @end deftypefn

function A = magic (n)

  if (nargin != 1)
    print_usage ();
  endif

  n = fix (n);
  if (n < 0)
    error ("magic: N must be non-negative");
  elseif (n < 1)
    A = [];
  elseif (mod (n, 2) == 1)

    shift = floor ((0:n*n-1)/n);
    c = mod ([1:n*n] - shift + (n-3)/2, n);
    r = mod ([n*n:-1:1] + 2*shift, n);
    A(c*n+r+1) = 1:n*n;
    A = reshape (A, n, n);

  elseif (mod (n, 4) == 0)

    A = reshape (1:n*n, n, n)';
    I = [1:4:n, 4:4:n];
    J = fliplr (I);
    A(I,I) = A(J,J);
    I = [2:4:n, 3:4:n];
    J = fliplr (I);
    A(I,I) = A(J,J);

  elseif (mod (n, 4) == 2)

    m = n/2;
    A = magic (m);
    A = [A, A+2*m*m; A+3*m*m, A+m*m];
    k = (m-1)/2;
    if (k > 1)
      I = 1:m;
      J = [2:k, n-k+2:n];
      A([I,I+m],J) = A([I+m,I],J);
    endif
    I = [1:k, k+2:m];
    A([I,I+m],1) = A([I+m,I],1);
    I = k + 1;
    A([I,I+m],I) = A([I+m,I],I);

  endif

endfunction


%!test
%! for i = 3:30
%!   A = magic (i);
%!   assert (norm(diff([sum(diag(A)),sum(diag(flipud(A))),sum(A),sum(A')])),0);
%! endfor

## Not a magic square but we must return something (bug #46672).
## While one day we may change the actual return of magic (2),
## this properties still must be true.
%!test <*46672>
%! m = magic (2);
%! assert (size (m), [2 2]);
%! assert (m, [4 3; 1 2]);

%!assert (isempty (magic (0)))
%!assert (magic (1), 1)
%!assert (magic (1.5), 1)

## Test input validation
%!error magic ()
%!error magic (1, 2)
%!error <N must be non-negative> magic (-5)

使用也特别容易，magic（3）

magic(3)
ans =

   8   1   6
   3   5   7
   4   9   2

查看帮助：

man magic
error: 'man' undefined near line 1, column 1
octave:9> help magic
warning: tempdir: '/tmp/' does not exist or is not a directory
warning: called from
    tempdir at line 48 column 5
    __makeinfo__ at line 135 column 17
    help at line 109 column 24

'magic' is a function from the file /usr/share/octave/6.4.0/m/special-matrix/magic.m

 -- magic (N)

     Create an N-by-N magic square.

     A magic square is an arrangement of the integers '1:n^2' such that
     the row sums, column sums, and diagonal sums are all equal to the
     same value.

     Note: N must be a scalar greater than or equal to 3.  If you supply
     N less than 3, magic returns either a nonmagic square, or else the
     degenerate magic squares 1 and [].

Additional help for built-in functions and operators is
available in the online version of the manual.  Use the command
'doc <topic>' to search the manual index.

Help and information about Octave is also available on the WWW
at https://www.octave.org and via the help@octave.org
mailing list.

通过系统函数magic的源码明显看出m函数有几个部分：

1、函数定义： function  [返回变量列表(多个变量之间用逗号分割)]  = 函数名称(言简意赅，顾名思义即可)(输入变量列表(多变量之间用逗号隔开))

2、帮助文本：第1行叫做H1行帮助文本，有特殊作用，经常用来说明函数的功能，版权等信息

3、函数主题：函数体语句段，%后边的是注释语句

4、函数最后的end语句，可以省略

说明：函数定义中function关键字、函数名称和参数列表的括号，其他都可以省略，其中函数名可以自己按照标识符的要求自己编写，其他都是不能乱改的。

对每一个函数，m环境自动生成两个变量nargin和nargout实现变量检测，无需声明可以直接使用

子函数一般位于主函数中，常常位于非第一个函数的位置，可以被主函数或其他子函数调用

主函数一般位于函数的第一个位置，函数名称于文件名称一般同名

%剔除向量a的奇异数据,系统的测量精度为可设置cal                              
function remainP = distriMethodV2(a, cal)
    b = sort(a);                                            %向量数据排序    xm = getXm(b);                                          %获取向量的中位>值    fl = b(1:ceil(length(b)/2));
    if rem(length(b), 2) == 0
        fl = [fl xm];
    end
    fll = getXm(fl);

    if rem(length(b), 2) ~= 0
        fu = b(ceil(length(b)/2) : length(b));
    else
        fu = [xm, b((length(b)/2 + 1) : length(b))];
    end
    fuu = getXm(fu);

    remainP = b(find(abs(b) <= cal*(fuu - fll)));

    %求向量中位值    function xm = getXm(b)
        if rem(length(b), 2) ~= 0
            index = ceil(length(b)/2);
            xm = b(index);
        else
            index = length(b)/2;
            xm = (b(index) + b(index + 1))/2;
        end

function mul = multiV2(a)                                                   
    mul = 1;
    for i = 1 : length(a)
        mul = mul * a(i);
    end 

也可以：

function mul = multi(varargin)                                              
    mul = 1;
    for i = 1 : length(varargin)
        mul = mul * varargin{i};
    end