MATLAB: How to declare a function using the diff-command

diff()function declaration

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.

Best Answer

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.
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