Noise interface and definitions :
vector freq = {1,1,1};
vector offset = {0,0,0};
float amp = 0;
int turb = 5;
float rough = 0.5;
float atten = 1;
onoise(@P*freq - offset, turb, rough, atten)
* ampsnoise(@P*freq - offset, turb, rough, atten) * ampanoise(@P*freq - offset, turb, rough, atten) * amp
vop_simplexNoiseVF(@P*freq - offset, turb, rough, atten) * amp
vop_simplexNoiseVV(@P*freq - offset, turb, rough, atten) * amp
vop_perlinNoiseVF(@P*freq - offset, turb, rough, atten) * amp
vop_perlinNoiseVV(@P*freq - offset, turb, rough, atten) * amp
copied from https://www.timucinozger.com/post/2015/07/24/noise-with-vex