if else condition not working as expected in python's scipy code

问题

I'm defining a function for solving my differential equations in scipy's solve_ivp.

def conv(t,Z):
    global sw,von,X

    if sw==0 and X[1]>=von or sw==1 and X[0]>0:
            zdot=LA.inv(v1).dot(A1).dot(v1).dot(Z).reshape(4,1)+LA.inv(v1).dot(B1).dot(U)
            sw=1
            von=0.7
            X=v1.dot(Z)
    else:
            zdot= LA.inv(v0).dot(A0).dot(v0).dot(Z).reshape(4,1)+LA.inv(v0).dot(B0).dot(U)
            sw=0
            X=v0.dot(Z)
    return np.squeeze(np.asarray(zdot)) 

and solving my equation using

sw=0
e1,v1=LA.eig(A1)
von=0
Z= np.array([0, 0, 0, 0])
X=v1.dot(Z)
U = np.array([[vin], [vdon]])
Z0= np.array([0, 0, 0, 0])
V=v1
sol = solve_ivp(conv, tspan,Z0,method='Radau')

Initially as sw=0 and X =[0,0,0,0] , I expect the if condition to be satisfied and the if block to be implemented. But the program is executing the else block.I'm not able to understand the problem.

回答1:

According to Python Zen N2 "Explicit is better than implicit"

def conv(t,Z):
    global sw,von,X

    if sw==0 and (X[1]>=von or (sw==1 and X[0]>0)):
            zdot=LA.inv(v1).dot(A1).dot(v1).dot(Z).reshape(4,1)+LA.inv(v1).dot(B1).dot(U)
            sw=1
            von=0.7
            X=v1.dot(Z)
    else:
            zdot= LA.inv(v0).dot(A0).dot(v0).dot(Z).reshape(4,1)+LA.inv(v0).dot(B0).dot(U)
            sw=0
            X=v0.dot(Z)
    return np.squeeze(np.asarray(zdot)) 

Then debugger is the best way to find why you have True or (False and (False)) I may see from the values you have already provided that

• (sw==1 and X[0]>0) is equal to False because X[0]=0 in your initial condition

• You have not mentioned what is the value of von in the (X[1]>=von)

But based on results you get von is greater than 0. Check that and make explicit comparisons in the code. This will help a lot in the future.

来源：https://stackoverflow.com/questions/61498295/if-else-condition-not-working-as-expected-in-pythons-scipy-code