You should give an array of config or an ini config file(see Yaf_Config_Ini) path to Yaf_Application::__construct().
Yaf will merge the application configurations and user configurations automatically. The application configurations have prefix "yaf." or "application.". If both "yaf." and "application." exist, "application." will be accepcted preferentially.
Example #1 An PHP array example
<?php
    $configs = array(
            "application" => array(
                "directory" => dirname(__FILE__),
                "dispatcher" => array(
                      "catchException" => 0,
                    ),
                "view" => array(
                       "ext" => "phtml",
                    ),
                ),
           );
    $app = new Yaf_Application($config);
?>
Example #2 An ini file example
[yaf] yaf.directory = APPLICATION_PATH "/appliation" yaf.dispatcher.catchException = 0 [product : yaf] ; user configuration list here
| Name | Default | Changelog | 
|---|---|---|
| application.directory | ||
| application.ext | "php" | |
| application.view.ext | "phtml" | |
| application.modules | "index" | |
| application.library | application.directory . "/library" | |
| application.library.directory | application.directory . "/library" | |
| application.library.namespace | "" | |
| application.bootstrap | application.directory . "/Bootstrap" . application.ext | |
| application.baseUri | "" | |
| application.dispatcher.defaultRoute | ||
| application.dispatcher.throwException | 1 | |
| application.dispatcher.catchException | 0 | |
| application.dispatcher.defaultModule | "index" | |
| application.dispatcher.defaultController | "index" | |
| application.dispatcher.defaultAction | "index" | |
| application.system | 
Here's a short explanation of the configuration directives.
application.directory
      string
     The directory of the application, that is the folder which contains the "controllers", "views", "models", "plugins" folders.
Note:
This config entry is the only one which doesn't has a default value. You should always define it manually.
application.ext
      string
     The file ext of the PHP script, used in class autoloading( Yaf_Loader).
application.view.ext
      string
     The file ext of the view template scripts.
application.modules
      string
     A comma-separated list of the registered modules, used in the route process, especially while there are more than three segments in the PATH_INFO,
Yaf need a way to find out whether the first segment is a module name or not.
application.library
      string
     The local library directory, see Yaf_Loader and yaf.library.
Note:
After Yaf 2.1.6, this config entry can be an array. The library path will try to use the items setted in application.library.directory
application.library.directory
      string
     Alias of application.library. Introduced in Yaf 2.1.6
application.library.namespace
      string
     A comma-separated prefix of local library namespace.
Introduced in Yaf 2.1.6
application.bootstrap
      string
     A absolute path of the Bootstrap class script.
application.baseUri
      string
     Used to remove a fixed prefix of request uri in route process. Take a example, comes a request with request uri "/prefix/controller/action". if you set application.baseUri to "/prefix", then only "/controller/action" will take as the PATH_INFO in route process.
In generally, there is no need to set this value.
application.dispatcher.throwException
      bool
     If it set to On, Yaf will throw an exception while some error occurring. See also Yaf_Dispatcher::throwException().
application.dispatcher.catchException
      bool
     If it set to On, Yaf will forward to Error controller/Action while there is an unhandled exception. See also Yaf_Dispatcher::catchException().
application.dispatcher.defaultRoute
      string
     The default Route, if it is not specificed, Static route will be used as default. See: Yaf_Router::addRoute().
application.dispatcher.defaultModule
      string
     The default module name, see also Yaf_Dispatcher::setDefaultModule().
application.dispatcher.defaultController
      string
     The default controller name, see also Yaf_Dispatcher::setDefaultController().
application.dispatcher.defaultAction
      string
     The default action name, see also Yaf_Dispatcher::setDefaultAction().
application.system
      string
     Set yaf runtime configure in application.ini, like: application.system.lowcase_path
Note:
only those PHP_INI_ALL configures can be set in this way