Module 

Header 
/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h 
Include 
#include "Math/UnrealMathUtility.h" 
static float SmoothStep
(
float A,
float B,
float X
)
Returns a smooth Hermite interpolation between 0 and 1 for the value X (where X ranges between A and B) Clamped to 0 for X <= A and 1 for X >= B.
Smoothed value between 0 and 1
Parameter 
Description 

A 
Minimum value of X 
B 
Maximum value of X 
X 
Parameter 