I have to solve these systems in succession, and I don't know how:
I need P and Q
P = transpose[(p1,p2,p3)]
Q = transpose[(q1,q2,q3)]
-p1+p2-p3 = 1
p2 - p3 = 1
-----------------
p1 = 0, p2 = 1+p3
~~~~~~~~~~~~~~~~~
-q1+q2-q3 = p2
q2 - q3 = p3
----------------
-q1 = p2-p3 = 1 --------> q1= -1
q2 = p3 + q3
P = transpose[(0, 1+p3, p3)]
Q = transpose[(-1, p3 + q3, q3)]
which means you've got 2 D.O.F's let's choose for instance q3 = p3 = 0
P = transpose[(0,1,0)] Q = transpose[(-1,0,0)]