Several figures with subplots using a combination list in Matplotlib - matplotlib

Question

I want to make a streamplot of a vectorial field which contains some free constants which I would like to change. So I've made combinations of these constants and I can sucessfully plot the stream plots one by one with this:
Y, X = np.mgrid[-1:10:200j, 0:10:200j]
tau_x = [0.01, 0.1, 1., 10.]
tau_y = [0.01, 0.1, 1., 10.]
alpha = [0.01, 0.1, 1., 10.]
r = [0.1, 0.01, 0.001]
K = [0.1, 0.5, 1.0, 1.5]
combinations_list = list(itertools.product(tau_x,tau_y,alpha,r,K))
for a in combinations_list:
(tau_x, tau_y, alpha, r, K) = a
Fx = (1/tau_x) * ( (-8/3)*(2*r-alpha)*(X-1) + K*X )
Fy = (2/(tau_y*X**(3/2))) * ( -2*(Y-1) + 3*Y*(X-1)/X + K*X*Y )
fig, ax = plt.subplots()
strm = ax.streamplot(X, Y, Fx, Fy, linewidth=0.5)
plt.show()
Now, because we are talking of a very large number of combinations, I would like to make a figure with subplots (say 9 each figure but it could be more) which would reduce a lot the number of figures.
Note: I am interested in seeing one figure each time and that's why plt.show() is inside the loop to avoid opening all figures at once.
EDIT: Following ImportanceOfBeingErnest sugestion I changed the code to
Y, X = np.mgrid[-1:10:200j, 0:10:200j]
tau_x = [0.01, 0.1, 1., 10.]
tau_y = [0.01, 0.1, 1., 10.]
alpha = [0.01, 0.1, 1., 10.]
r = [0.1, 0.01, 0.001]
K = [0.1, 0.5, 1.0, 1.5]
combinations_list = list(itertools.product(tau_x,tau_y,alpha,r,K))
length = len(combinations_list)
N = 9 #number of subplots per figure
for i in range(0,100):
subset = combinations_list[9*i:9*i+9]
fig = plt.figure()
j = 1
for a in subset:
(tau_x, tau_y, alpha, r, K) = a
Fx = (1/tau_x) * ( (-8/3)*(2*r-alpha)*(X-1) + K*X )
Fy = (2/(tau_y*X**(3/2))) * ( -2*(Y-1) + 3*Y*(X-1)/X + K*X*Y )
ax = fig.add_subplot(3,3,j)
ax.streamplot(X, Y, Fx, Fy, linewidth=0.5)
++j
plt.show()
but it's only plotting the first one of each subset and in a weird way with colors in the vectors.

Answer 1

You are not updating j correctly. ++j doesn't update the value of j. Your code will work fine if you replace ++j by j += 1 or j = j+1. Both are equivalent.
for i in range(0,100):
subset = combinations_list[9*i:9*i+9]
fig = plt.figure()
j = 1
for a in subset:
(tau_x, tau_y, alpha, r, K) = a
Fx = (1/tau_x) * ( (-8/3)*(2*r-alpha)*(X-1) + K*X )
Fy = (2/(tau_y*X**(3/2))) * ( -2*(Y-1) + 3*Y*(X-1)/X + K*X*Y )
ax = fig.add_subplot(3,3,j)
ax.streamplot(X, Y, Fx, Fy, linewidth=0.5)
j += 1 # <--- change here