How will put initial values in x0 of s-function that is in a matlab file (.m)?

I want to put the given function in x0 of s-function level 1:

function [ s0 ] = init_3d( )

phi0 = 0.0; theta0 = 0.0; psi0 = des_start.yaw; Rot0 = RPYtoRot_ZXY(phi0, theta0, psi0); Quat0 = RotToQuat(Rot0);

s0 = [des_start.pos des_start.vel Quat0 0 0 0];

end