[Python] Is there a way to specify which element of arrays I want to add via indexation?

massetest = np.array([12,15])
xtest = np.array([34,30])
ytest = np.array([1,0])
ztest = np.array([7,1])
rtest = np.array([xtest,ytest,ztest])
rtest = rtest.T

def integrateur(r,v,a,step):
v = v + a * step/2
r = r + v *step
a = acceleration(massetest,rtest,1)
v = v + a * (step/2)
v = v+ a * (step/2)
return r, v, a

v_r = np.ones((2,3))
acc = np.ones((2,3))

def acceleration(masse,r,G):
x = r[:,0:1]
y = r[:,1:2]
z = r[:,2:3]

dpos_x = x.T - x
dpos_y = y.T - y
dpos_z = z.T - z

nc = ( dpos_x**2 + dpos_y**2 + dpos_z**2)**(1.5)

ax = G*(dpos_x * masse)/nc
ay = G*(dpos_y * masse)/nc
az = G*(dpos_z * masse)/nc

a = np.array([ax,ay,az])
return a


a's shape is (3,2,2)
v's shape is (2,3)

I realize that I can't add them because of their shape but I can't seem to find a work around.

This is the error I get:

ValueError: operands could not be broadcast together with shapes (2,3) (3,2,2)


I tried to add only certain parts of a with v but I can't really access the ones I need and well I don't really end up with the values that are needed and that creates errors of their own kinda lost ngl.

I am trying to compute an n-body simulation but I am currently trialing with only 2 particules using the leap-frog integration method which is supposed to conserve the system's total energy.

Continue reading...