Design H-infinity controller in Matlab.

I used Sliding Mode Control technique to control the trajectory tracking of the vehicle, and the drawback to use the sliding mode control is in the form of chattering/ switching or so called high frequencies that will be generated. I want to reduce this chattering or high frequency by using H-Infinity method. So, the H-infinity Controller is required for Sliding Surface Design. Basically, H-infinity controller works on sliding surface that adjust the gains and reduce the chattering or so called high frequencies. For my work I used S-Function in Mat lab to write a program. So, I need H-Infinity program in S-Function (Matlab).