Octave教程（五）

控制语句

V =   0   0   0   0   0   0   0   0   0   0>> for i=1:10,                 % for循环>     V(i) = 2 ^ i;> end;>> VV =      2      4      8     16     32     64    128    256    512   1024>> indices = 1:10;>> for i=indices,          % for循环遍历输出>     disp(i);> end; 1 2 3 4 5 6 7 8 9 10>> i = 1;>> while i <= 5,              % while循环>     V(i) = 100;>     i = i + 1;> end;>> VV =    100    100    100    100    100     64    128    256    512   1024>>  i = 1;>> while true,>     V(i) = 999;>     i = i + 1;>     if i == 6,>         break;              % break与continue的使用>     end;> end;>> VV =    999    999    999    999    999     64    128    256    512   1024>> V(1) = 2;>> if V(1) == 1,                             % if-else语句>     disp('The value is one');> elseif V(1) == 2,>     disp('The value is two');> else>     disp('The value is not one or two');> end;The value is two

函数

我们先创建costFunctionJ.m文件，并在其添加如下代码：

function J = costFunctionJ(X, y, theta)% X is the "design matrix" contanining our tranining examples.% y is the class labels.m = size(X, 1);                   % number of tranining examplespredictions = X*theta;            % predictions of hypothesis on all m examplessqrErrors = (predictions-y).^2;   % squared sqrErrorsJ = 1/(2*m) * sum(sqrErrors);

然后，我们在Octave的CLI中键入如下命令：

% 先利用cd命令前往costFunctionJ.m文件目录路径>> X = [1 1; 1 2; 1 3]X =   1   1   1   2   1   3>> y = [1; 2; 3]y =   1   2   3>> theta = [0;1];>> j = costFunctionJ(X, y, theta)j = 0

注：文件名需与函数名一致。