How to declare a function using the diff-command

In Matlab I am given a function whose declaration starts with this code:

function [v1, v2, v3, v4, v5, v6] = calculate_v(P1, P2, angle, difference) 

dP1=P1(2) - P1(1);
dangledP1=diff(angle)/dP1;
dP2dP1=diff(P2)/dP1;

But I don't understand it. The input variables seem to be vectors. I know the diff-command returns a vector whose entries are the difference of adjacent entries. But what is happening in the first line:

dP1 = P1(2) - P1(1) ?

I mean does P1 only have two entries? I am not given any further information about the variables either.

Answer 1

[KSSV]

You have to enter at least two entries for P1, dP1=P1(2) - P1(1) is like calculating the difference/ step. If you enter more then two elements also, your code will not take the other values into consideration.

[Luki]

Ok. So the difference to diff(P1) is that P1(2)-P1(1) would only equal the first entry of diff(P1)

[KSSV]

No diff(P1) calculates the difference P(i)-P(i+1)..._diff_ calculates the difference among the successive elements and it's size would be one less then the input vector. In your code there is no diff(P1).