CODEWITHSUNDEEP
pythonloops
Amsterdoom
Amsterdoom

Reputation: 15

Python nested loop behaviour

i'm new to python and I think there is something I don't understand with how nested loop work. I have this nested loop that should run multiple times until precision eps is reached but it exits after running once. I tried debugging and realized that when the epoch +=1 incrementation line is reached, w and w_last are both modified by the 2nd loop and are equal. I don't understand why this is the case since only w should be modified by the second loop. I have the same problem using a for loop. There is something I don't understand, maybe someone can point it out

while(all(abs(w - w_last)) >= eps) :
  w_last = w
  sum_error = 0
  j = 0
  while j < n_data :
     y_pred[j] = w[0]+ (w[1]*x[j])
     error = y_pred[j] - y[j]
     sum_error += error**2
     w[0] = w[0] - step * error
     w[1] = w[1] - step * error * x[j]
     j += 1
  epoch += 1
  print('>epoch=%d, step=%.4f, error=%.3f' % (epoch, step, sum_error))
print(w)

w is a (2,1) numpy array of weights epoch keeps track of the number of time I run through the data (2nd loop)

Thank you!

Upvotes: 1

Views: 113

Answers (1)

DYZ
DYZ

Reputation: 57105

w_last = w makes another reference to w, not a copy of it. You must use w_last = w.copy().

Upvotes: 2

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