看不懂有关 nargin 的程序代码

sun1993

John H. Mathews著的数值方法（matlab版）中第308页有个求极小值的单纯形法程序，
一开始的　if nargin==5
                 show=0;
              end
    %show==1displays iterations(P and Q)
没弄明白，这是用来做什么呀？
各位大侠，能否教我一下？谢谢！

[ 本帖最后由 eight 于 2007-8-28 18:56 编辑 ]

jimin

nargin, nargout
Purpose
Number of function arguments.

Synopsis
n = nargin
n = nargout

Description
In the body of a function M-file, nargin and nargout indicate how many input or output arguments, respectively, a user has supplied.
nargin returns the number of input arguments specified for a function.

nargout returns the number of output arguments specified for a function.

Examples
This example shows portions of the code for the function fplot, which has an optional number of input and output arguments:

function [x0,y0] = fplot(fname,lims,npts,angl,subdiv)
%FPLOT Plot a function.
% FPLOT(fname,lims,npts,angl,subdiv)

% The first two input arguments are
% required; the other three have default values.
...
% [x,y] = fplot(...) returns x and y instead
% of plotting them.
...
if nargin < 5, subdiv = 20; end
if nargin < 4, angl = 10; end
if nargin < 3, npts = 25; end
...
if nargout == 0
plot(x,y)
else
x0 = x;
y0 = y;
end

jimin

nargin用法示例。
    函数文件examp.m：
function fout=charray(a,b,c)
if nargin==1
   fout=a;
elseif nargin==2
   fout=a+b;
elseif nargin==3
   fout=(a*b*c)/2;
end
    命令文件mydemo.m：
x=[1:3];
y=[1;2;3];
examp(x)
examp(x,y')
examp(x,y,3)

sun1993

好厉害，谢谢！:@D

xjzuo

简单讲,就是判断输入变量个数.------help nargin 即知．