# Moving platform algorithm
**URL:** https://discussions.unity.com/t/moving-platform-algorithm/418602
**Category:** Scripting
**Tags:** Scripting
**Created:** [July 20, 2010, 4:07pm UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602 "2010-07-20T16:07:30Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@anon\_97027186](https://discussions.unity.com/u/anon_97027186)
#### Post date: [July 20, 2010, 4:07pm UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602/1 "2010-07-20T16:07:30Z")
Hi!
I’m running through the 2D tutorial made by Unity3D team. The forumula they use to move the platform is this:
```auto
var weight = Mathf.Cos(Time.time * speed * 2 * Mathf.PI) * 0.5 + 0.5;
transform.position = targetA.transform.position * weight + targetB.transform.position * (1-weight);
```
I understand the first line that get the “weight” or the oscillation, but can anyone tell me where the second formula comes from? Some vector math theorem or what?
---
### Author:  [@j\_y\_k](https://discussions.unity.com/u/j_y_k)
#### Post date: [July 20, 2010, 5:58pm UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602/2 "2010-07-20T17:58:47Z")
The second formula is simple linear interpolation (usually referred to as LERP).
(Also, I think Unity may already have a LERP function for vectors…)
---
### Author:  [@anon\_97027186](https://discussions.unity.com/u/anon_97027186)
#### Post date: [July 21, 2010, 9:39am UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602/3 "2010-07-21T09:39:02Z")
Thanks, but while reading about LERP at [wikipedia](http://en.wikipedia.org/wiki/Lerp_%28computing%29) I couldn’t find anything that would lead me to that forumula used in the tutorial mentionend.
Any more hints? I would love how to understand how this formula was deduced.
Edit: I understand that the new vector (transform.position) can be “build” from adding a fraction of vector A (targetA) and vector B (targetB). But I’m looking for why this fraction is **weight** and **1-weight**
---
### Author:  [@j\_y\_k](https://discussions.unity.com/u/j_y_k)
#### Post date: [July 21, 2010, 5:11pm UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602/4 "2010-07-21T17:11:08Z")
> [@""](#):
>
> Thanks, but while reading about LERP at [wikipedia](http://en.wikipedia.org/wiki/Lerp_%28computing%29) I couldn’t find anything that would lead me to that forumula used in the tutorial mentionend.
The Wikipedia article is simply presenting LERP in a different context (that of a graph).
Try [this](http://gpwiki.org/index.php/Linear_Interpolation) instead. The formula given there is (I’m going to change the variable names for convenience):
```auto
p = A + t(B - A)
```
This formula basically ‘starts at A’, and then adds some amount of the difference between A and B to yield a point somewhere between A and B (assuming ‘t’ is in the range [0, 1]).
Now, let’s re-arrange this formula:
```auto
p = A + t(B - A)
p = A + tB - tA
p = tB + A - tA
p = tB + (1 - t)A
```
And we have the formula shown in your code example.
Another way to think of it is this. When ‘t’ is 0, you can see that we get ‘all’ of A and ‘none’ of B. Conversely, when ‘t’ is 1, we get ‘all’ of B and ‘none’ of A. Values of ‘t’ between 0 and 1 give us (in a linear progression) ‘some’ of A and ‘some’ of B. As ‘t’ increases, we get more B and less A (again, in a linear progression).
Does that make more sense?
---
### Author:  [@anon\_97027186](https://discussions.unity.com/u/anon_97027186)
#### Post date: [July 22, 2010, 9:19am UTC](https://discussions.unity.com/t/moving-platform-algorithm/418602/5 "2010-07-22T09:19:03Z")
Yes and thanks a million! 🙂
Edit: And thanks for guiding me to that wiki, didn’t know about it before.