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Should the weights of a neural network without hidden layer and a logistic activation function be the same as the parameters of a logistic regression? Mine are not the same?

nnallnohidden=nnet(
    PartialPrepayzo~FIXPER+MEDSAL2+DREL+LEEFTIJD+HH2CRED+LTV_curr+
    rate1Y+rate5Y+CIremFIRP+URB+WELSTAN2+OutNot+mover+SavRate+CRate,
    data=test,
    size=0,
    skip=T)

log <- glm(PartialPrepayzo~FIXPER+MEDSAL2+DREL+
LEEFTIJD+HH2CRED+LTV_curr+rate1Y+rate5Y+CIremFIRP+URB+WELSTAN2+OutNot+mover+SavRate+CRate, data = test, family = "binomial")
summary(log)

                 [,1]           [,2]
 [1,] -1.029560622391 -1.26664018566
 [2,] -0.078225500455 -0.06536644222
 [3,]  0.410455341173  0.67036107254
 [4,]  0.006961510972 -0.11463794856
 [5,]  0.473629162069  0.70074482878
 [6,]  0.614550199698  0.83536187570
 [7,] -0.612837570442 -0.48086112696
 [8,] -0.743739495966 -1.06994471577
 [9,]  0.200419240204  0.83957097597
[10,] -0.166568966328 -0.50583277715
[11,]  0.017640270701  0.12678131085
[12,] -0.005947704128 -0.04248886193
[13,] -0.428175932694 -1.69521649738
[14,]  0.049657239050  0.26482261363
[15,]  1.602200661890  2.50479250068
[16,]  0.367771764513  0.96127873663
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    $\begingroup$ No shouting in titles please. $\endgroup$
    – Nick Cox
    Aug 20, 2013 at 12:09
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    $\begingroup$ nnet() by default optimizes squared error instead of binomial loss. Try using entropy=TRUE to have it optimize the same loss function as logistic regression. $\endgroup$ Aug 20, 2013 at 13:08
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    $\begingroup$ It also looks like you have a fair number of features; I'd try something like an elastic net penalty from the glmnet package to see if any of those fall out. You can do a pure ridge penalty in nnet() using the weight parameter (but would have to optimize it via resampling). $\endgroup$ Aug 20, 2013 at 13:10
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    $\begingroup$ If you have lost your login credentials, please follow instructions in our Help Center to merge your different accounts. Sidenote: It is a bad idea to rollback changes that are made by benevolent users who are just willing to help and improve your post. $\endgroup$
    – chl
    Aug 20, 2013 at 16:23

1 Answer 1

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Reproducing comments:

  • Shea Parkes: nnet() by default optimizes squared error instead of binomial loss. Try using entropy=TRUE to have it optimize the same loss function as logistic regression.

Also, to reproduce a logistic regression, you need the input to output activations to be linear, but the readout layer to predict probabilities. This is because the logistic regression is estimating a linear function of the inputs. The readout layer piece is accomplished by Shea’s comment, but you’ll also need to adjust the internal activations.

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