app/code/local/Bendart/Matrix/etc/config.xml

config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Bendart_Matrix>
            <version>0.1.0</version>
        </Bendart_Matrix>
    </modules>
    <global>
        <models>
            <catalog>
                <rewrite>
                    <product_type_configurable>Bendart_Matrix_Catalog_Model_Product_Type_Configurable</product_type_configurable>
                </rewrite>
            </catalog>
        </models>
    </global>
    <frontend>
        <layout>
            <updates>
                <matrix>
                    <file>matrix.xml</file>
                </matrix>
            </updates>
        </layout>
        <routers>
            <matrix>
                <use>standard</use>
                <args>
                    <module>Bendart_Matrix</module>
                    <frontName>matrix</frontName>
                </args>
            </matrix>
        </routers>
    </frontend>
</config>