use yii\helpers\Inflector; $string = 'my_string_variable'; $camelCaseString = Inflector::camelize($string); echo $camelCaseString; // outputs "myStringVariable"In this example, we first include the Inflector utility class from the Yii helpers package. We then define a string variable in underscore notation. We use the camelize function to convert the string to camelcase notation, and then we output the result. This function is commonly used in programming languages like Java and JavaScript, and this functionality is also available in the PHP Yii framework. It is part of the Yii utilities package, and can be found in the yii\helpers\Inflector class.