Questions tagged [sigmoid-curve]

A sigmoid function is a mathematical function having a characteristic "S"-shaped curve or sigmoid curve. Often, sigmoid function refers to a special case of the logistic function. It is closely related to the logistic regression.

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how many methods are there to find logistic regression [closed]

1 ) I'm confused between different terminology in logistic regression . "Legit Function , Sigmoid Function , maximum likelyhood ...." 2) Im learning ML , How much math knowledge about Logistic ...
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Understanding interpolation results in a sigmoid regression

I have a doubt about the results I got from an interpolation even though it was performed by a statistical software (SigmaPlot). I have the variable X that is the time expressed in hours and the ...
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Calculate LC50 from a non-sigmoid dose response curve

Is it possible to calculate LC50 (concentration that is lethal for 50% of the test organisms), when my dataset does not have a sigmoid dose response curve? For my experiment, I had 6 treatments ...
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Can we use perceptron training algorithm to train a single neuron with sigmoid activation?

The perceptron training algorithm is summarized as: Apply the inputs and calculate the output $ y $ Compare with the desired output yd and calculate error $e = y-y_d$ Update the weights based on the ...
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How is the output bias decided when using sigmoids to approximate functions

In this link : http://neuralnetworksanddeeplearning.com/chap4.html It has been said that, to approximate functions, the output bias has to be (−m+1/)h. Here is a snapshot of that part: I do ...
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Why are only activations used in softmax set to zero and not the weight matrix during initial phase of learning in neural networks?

I am reading Understanding the difficulty of training deep feed-forward neural networks. While the whole paper itself is very tough, there is one section is particularly not making sense to me. Some ...
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How to normalize the output of a neural network [duplicate]

We have a VGG16 network trained from scratch with a Sigmoid output function. We have 6 classes and the usual output looks like this: ...
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How to adjust the activation function to output y values more than 1?

This link introduces a neural network to solve a classification problem. It uses the sigmoid function as the activation function for both of the two layers (one hidden and one output layer). Can I ...
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With Sigmoid activation and Softmax normalization with cross entropy, are we fitting distributions?

Let's consider I have a multi layer neural network that is doing multi class classification. So each input sample belongs to one on N classes. Now, lets say the last layer has Sigmoid activation ...
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Convnet learning: all weights tend to zero and left only with bias

I am working on a conv net that deals with a classification problem and wonder what sort of mistake I am making to get this sort of problem? I have nine outputs - I can't use softmax as the nature of ...
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Glorot/ Xavier Init: for sigmoid and tanh?

My question is about Xavier Glorot Init. The assumptions that they make are that they approximate the activation function linearly, that this function has f'(0) = 1 and that we set the bias to 0, as ...
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Is there something like softmax but for top k values?

I have a dataset with binary labels of which exactly k outputs are 1, on which I want to train a neural network. If k=1, softmax can do the job of representing the output distribution. I am interested ...
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Why does the scaled probit function coincide with the logistic sigmoid function at lambda = pi/8?

I'm currently working through through "Pattern Recognition and Machine Learning" by Christopher Bishop, and chanced upon this question while working towards my finals: My two questions are: ...
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What is the interpretation of the “C” parameter in the five parameters logistic curve?

I'm using the following equation for the 5-parameters logistic curve: $$ y = A + \frac{D-A}{\Bigl(1+\exp\bigl(B(C-x)\bigr)\Bigr)^S} $$ What is the interpretation of the $C$ parameter? I found some ...
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87 views

Generate odds ratios across deciles / quantiles of an indpendent variable

With reference to the following figure from Bellomo et al., 2011: How exactly are the odds ratios across the deciles 'referenced against the 4th decile' calculated? My initial impression is that a ...
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LSTM cell state update equation wrong in Deep Learning book? (Equation 10.41)

In Equation 10.41 of the Deep Learning Book, the author writes the update equation of LSTM cell internal state as : $$ s_{i}^{(t)}=f_{i}^{(t)} s_{i}^{(t-1)}+g_{i}^{(t)} \sigma\left(b_{i}+\sum_{j} U_{...
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How to aggregate calibration curves which were created in cross validation?

When looking into Scikit's CalibratedClassifierCV I noticed that the object needs to keep multiple calibrated classifiers in memory to average the results in real time. I understand that these ...
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Can the vanishing gradient problem be solved by multiplying the input of tanh with a coefficient?

To my understanding, the vanishing gradient problem occurs when training neural networks when the gradient of each activation function is less than 1 such that when corrections are back-propagated ...
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Logistic function with a slope but no asymptotes?

The logistic function has an output range 0 to 1, and asymptotic slope is zero on both sides. What is an alternative to a logistic function that doesn't flatten out completely at its ends? Whose ...
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How can I even out the output of the sigmoid function?

I'm applying a sigmoid function to an array of values but the output is very concentrated near 1 (i.e. 25th percentile is 0.999). I think this is because the input array takes on values that are quite ...
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69 views

Is there a Gaussian Process Kernel that limits functions to sigmoids?

I am modeling a large number of Dose-response curves. I have strong reason to believe that the generating function will be sigmoidal against the concentration of the assay (Michaelis-Menten kinetics). ...
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161 views

Counting the number of neural network parameters [duplicate]

I am slightly confused by counting the number of NN parameters. Let's assume there is a NN with 4-dim vector as an input, then comes 5-dim hidden layers, and another one 6-dim hidden layer. There is a ...
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How to convert IRT theta score to a percentage score

I am trying to implement an adaptive test using 3PL IRT model. We need to screen the candidates and label their expertise as ...
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When is logit function preferred over sigmoid?

I found out that logit and sigmoid functions are inverse of one another, and are used in binary classification, but is there a preference of one over another in any circumstances, or can they be used ...
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Does mixture of sigmoids make sense given the theories about mixture of bernoullis?

Mixture of bernoullis is the combination of bernoulli distributions, which can be illustrated by the sampling process of K bags of D coins, here is a quick tutorial about it https://cedar.buffalo.edu/~...
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Softmax weights initialization

I am a new to deep learning and neural networks, and I need to know if there is a good weights initialization method to use if the activation function is Softmax like Tanh, ReLU and Sigmoid. Related ...
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389 views

Compare two sigmoid shape curves

I have x and y-values for two sigmoid curves (probit). x-values are the same for both curves,...
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664 views

Does it make sense to use `logit` or `softplus` loss for binary classification problem?

With $z$ is the logit, $p \in \{1, 0\}$ is the class. Usually binary classification problem use sigmoid and cross-entropy to compute loss: $$\mathcal{L_1} = - \sum{p \log \sigma(z) + (1-p) \log (1-\...
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Has Arcsinh ever been considered as a neural network activation function?

The function $y = arcsinh(x)=ln(x+\sqrt{x^2+1})$ has some nice features that I could imagine being useful as an activation function in a neural network. It has sigmoid behaviour around zero, but far ...
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Question about Sigmoid Function in Logistic Regression

This is with reference with Andrew Ng's video on Logistic Regression, I just want to confirm a small doubt I have. I get the basic idea of Logistic Regression that $z=\theta^Tx$ Where $\theta$= ...
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How does Bayes' rule on two exponentials suggest a sigmoid?

In Platt's 1999 paper on turning support vector machine output into a probabilistic score, he says Bayes rule on two exponentials suggests using a parametric form of a sigmoid where he cites this ...
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Finding the slope at different points in a sigmoid curve

This is my data. x <- c(0.5,3.0,22.2,46.0,77.3,97.0,98.9,100.0) plot(x, pch = 19) I want to fit a curve through these points and then calculate the slope at ...
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Why do we use the natural exponential in logistic regression?

I would like to intuitively understand the benefit of using the natural exponential in the sigmoid function used in logistic regression. Why should it have to be $e^x$ instead of, for example $2^x$?
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Why is tanh almost always better than sigmoid as an activation function?

In Andrew Ng's Neural Networks and Deep Learning course on Coursera he says that using $tanh$ is almost always preferable to using $sigmoid$. The reason he gives is that the outputs using $tanh$ ...
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logistic regression - why we forget assumption on data?

I read logistic regression formula i.e. $ \log\frac{P(C_1|X)}{P(C_2|X)}=w^Tx+w_o$ but this equation is true if we have $P(X|C_1)$ and $P(X|C_2)$ sampled from two Gaussian with the same covariance ...
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Difference between logistic regression models for classification problems

In various papers, I had often seen the logistic regression model for classification problems written in two forms. $$p(y =\pm1|\mathbf{x},\mathbf{w}) = \sigma(y\mathbf{w}^{T}\mathbf{x}) = \frac{1}{1+...
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Expected value of softmax transformation of Gaussian random vector

Let $\mathbf w_1,\mathbf w_2,\ldots,\mathbf w_n \in \mathbb R^p$ and $\mathbf v \in \mathbb R^n$ be fixed vectors, and $\mathbf x \sim \mathcal N_p(\boldsymbol{\mu}, \mathbf{\Sigma})$ be an $p$-...
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Finding the center of a logistic curve

Given a sigmoidal/logistic curve p what's the general procedure to finding at what value of x is the curve centered?
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How to model positive S-shaped-function? [closed]

I need to transform my data into a function shown below. My data should fit in the range from 0 to 1. The inflection point should be on 0.5. How I can do this mathematically? Is there any similar ...
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334 views

Modification of Sigmoid function

I need to model my data into a function like shown in the following picture. But how I can do this mathematically? Is there any similar function to model data that should increase on smaller values ...
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301 views

What is the difference between a logistic curve and something that overshoots?

In population dynamics, the growth of a population can have exponential growth, or a logistic curve growth up to its carrying capacity, or it can overshoot the carrying capacity and fluctuate before ...
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Approximation of Δoutput in context of Sigmoid function

I am currently learning the very basics of Machine Learning. This e-book looks quite helpful, but I am stuck at the first chapter already. There, the sigmoid function is defined like normal (equation ...
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638 views

How to do LASSO regression with a dependent variable that is continuous between 0 and 1

I am trying to do a LASSO regression on some data. However, my dependent variable is between 0 and 1. How do I go about this? Do I just apply a sigmoid function to the regression output? This will ...
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Sigmoid equals softmax in Bernoulli distribution (binary classification problem)? [duplicate]

Apparently, the sigmoid function $\sigma(x_i) = \frac{1}{1+e^{-x_i}}$ is generalization of the softmax function $\text{softmax}(x_i) = \frac{e^{x_i}}{\sum_{j=1}^{n}{e^{x_j}}}$. As far I've understood, ...
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888 views

Effect of e when using the Sigmoid Function as an activation function

I'm writing my own neural net from scratch (using Clojure). For the activation function for the nodes, I'm using the Sigmoid Function. I was messing around manually creating "trained" nets based on ...
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How do I calculate output of a Neural Network?

I just started learning about ANNs about a week ago with no classical training. Just by watching videos and reading blogs/white papers, I've gotten this far. I have a question about the final output ...
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187 views

How to analyse growth rate in R?

Within the framework of an experiment I followed to growth rate of bird nestlings. I measured them every day for weight and tarsus. I have a number of continuous and categorical explanatory variables, ...
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Relu vs Sigmoid vs Softmax as hidden layer neurons

I was playing with a simple Neural Network with only one hidden layer, by Tensorflow, and then I tried different activations for the hidden layer: Relu Sigmoid Softmax (well, usually softmax is used ...
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Looking for function to fit sigmoid-like curve

I'm looking for a function to fit sigmoid-like curves, from experimental data points. The model (the function) doesn't matter, it doesn't have to be physically relevant, I just want to be able to ...