首次安装完matlab时，在导入授权后，打开发现一堆警告，各种命令不可用，大致内容如下：

Warning: C:\Program Files\MATLAB\R2012a\toolbox\local\pathdef.m not found.
Toolbox Path Cache is not being used. Type ‘help toolbox_path_cache’ for more info
Undefined function or variable ‘ispc’.
Warning: MATLAB did not appear to successfully set the search path. To recover for this session of MATLAB, type “restoredefaultpath;matlabrc”. To find out how to avoid this warning the next time you start MATLAB, type “docsearch problem path” after recovering for this session.
Warning: Duplicate directory name: C:\Program Files\MATLAB\R2012a\toolbox\local.
Warning: Initializing Handle Graphics failed in matlabrc.
This indicates a potentially serious problem in your MATLAB setup,
which should be resolved as soon as possible. Error detected was:
MATLAB:undefinedVarOrClass
Undefined variable “graphics” or class “graphics.internal.initializeMATLABRoot”.
Warning: Initializing Java preferences failed in matlabrc.
This indicates a potentially serious problem in your MATLAB setup,
which should be resolved as soon as possible. Error detected was:
MATLAB:UndefinedFunction
Undefined function ‘usejava’ for input arguments of type ‘char’.
> In matlabrc at 113
Warning: Failed to add default profiler filters.
> In matlabrc at 168
>> rtwintgt -setup
Undefined function ‘rtwintgt’ for input arguments of type ‘char’.

>> help toolbox_path_cache
Undefined function ‘help’ for input arguments of type ‘char’.

实际上是安装的时候路径出错，用管理员模式启动，然后执行这个命令：

restoredefaultpath;matlabrc

matlab执行环境变量恢复以后，系统正常可用。