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# Smoohtdamp NaN problem

I'm using smoothdamp in a scene. When i changed scene and return back to scene that i use smoothdamp, velocity returns NaN. How can i solve this problem?

My Script:

```
void Update()
{
if (transform.position.z == 0)
{
if (Input.GetMouseButtonDown(0))
{
firstPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition).x;
x1 = firstPosition;
}
if (Input.GetMouseButton(0))
{
mouseButtonUp = false;
secondPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition).x;
transform.localPosition += new Vector3(secondPosition - firstPosition, transform.localPosition.y, transform.localPosition.z);
if (transform.localPosition.x > leftLimit.position.x)
{
transform.localPosition = leftLimit.position;
}
else if (transform.localPosition.x < rightLimit.position.x)
{
transform.localPosition = rightLimit.position;
}
firstPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition).x;
}
if (Input.GetMouseButtonUp(0))
{
x2 = Camera.main.ScreenToWorldPoint(Input.mousePosition).x;
distance = x1 - x2;
mouseButtonUp = true;
}
if (mouseButtonUp)
{
if (distance > 5.5f)
{
float xPosition = Mathf.SmoothDamp(transform.localPosition.x, rightLimit.position.x, ref xVelocity, smoothTime);
transform.localPosition = new Vector3(xPosition, transform.localPosition.y, transform.localPosition.z);
if (Mathf.Abs(transform.localPosition.x - rightLimit.position.x) < 0.1f)
{
mouseButtonUp = false;
}
}
else if (distance < 5.5f && distance >= 0 && transform.localPosition.x >= 0)
{
float xPosition = Mathf.SmoothDamp(transform.localPosition.x, leftLimit.position.x, ref x1Velocity, smoothTime2);
transform.localPosition = new Vector3(xPosition, transform.localPosition.y, transform.localPosition.z);
if (Mathf.Abs(transform.localPosition.x - leftLimit.position.x) < 0.1f)
{
mouseButtonUp = false;
}
}
else if (distance < -5.5f)
{
float xPosition = Mathf.SmoothDamp(transform.localPosition.x, leftLimit.position.x, ref x2Velocity, smoothTime3);
transform.localPosition = new Vector3(xPosition, transform.localPosition.y, transform.localPosition.z);
if (Mathf.Abs(transform.localPosition.x - leftLimit.position.x) < 0.1f)
{
mouseButtonUp = false;
}
}
else if (distance > -5.5f && distance < 0 && transform.localPosition.x < 0)
{
float xPosition = Mathf.SmoothDamp(transform.localPosition.x, rightLimit.position.x, ref x3Velocity, smoothTime4);
transform.localPosition = new Vector3(xPosition, transform.localPosition.y, transform.localPosition.z);
if (Mathf.Abs(transform.localPosition.x - rightLimit.position.x) < 0.1f)
{
mouseButtonUp = false;
}
}
x2 = x1;
}
}
}
```

EDIT: I've considered your suggestion and didn't do the above operations until I pass some frames to get a sensible deltaTime value but that didn't help. I don't think deltaTime is 0 here. Maybe that would give a "divided by zero exception". But I'm getting a NaN value and a respective error.

Thanks for checking out!

**Answer** by Bunny83
·
Feb 11, 2012 at 02:04 PM

NaN (Not a Number) happens when you do some illegal operations such as dividing by zero, squareroot of a negative number. Here's a nice overview (watch out: the examples on this page are in C++).

In other words, nobody can really "answer" this question without knowing what you're doing... Some code would be useful. Feel free to edit your question.

*edit*

Just had a look at the SmoothDamp function and the only thing i could think of is that you set the last parameter, deltaTime, to 0.0 or Unity's Time.deltaTime returned 0.0.

This is the implementation of SmoothDamp:

```
// C#
public static float SmoothDamp(float current, float target, ref float currentVelocity, float smoothTime, float maxSpeed, float deltaTime)
{
smoothTime = Mathf.Max(0.0001f, smoothTime);
float num = 2f / smoothTime;
float num2 = num * deltaTime;
float num3 = 1f / (1f + num2 + 0.48f * num2 * num2 + 0.235f * num2 * num2 * num2
float num4 = current - target;
float num5 = target;
float num6 = maxSpeed * smoothTime;
num4 = Mathf.Clamp(num4, -num6, num6);
target = current - num4;
float num7 = (currentVelocity + num * num4) * deltaTime;
currentVelocity = (currentVelocity - num * num7) * num3;
float num8 = target + (num4 + num7) * num3;
if (num5 - current > 0f == num8 > num5)
{
num8 = num5;
currentVelocity = (num8 - num5) / deltaTime;
}
return num8;
}
```

**Answer** by SuperGoA
·
Mar 05, 2017 at 10:15 PM

Make sure your Time.timeScale is set to a non-zero value. I kept getting this error when loading a scene because I had set Time.timeScale = 0 when my player dies, and I never set it back to 1 if they reloaded the scene.

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