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From: http://www.csrdu.org/nauman/2010/06/25/regression-with-gradient-descent-in-low-level-matlab/
I just finished writing my first machine learning algorithm inMATLAB. The algorithm is based on Gradient Descent search for estimatingParameters of
Since the experimental report of the first experiment is not in this machine, write this algorithm first.SGDLR (The Stochastic Gradient descent for Logistic Regression), to explain this algorithm, first of all to split the name into a few pieces.1 Random 2 gradient descent 3
direction.3, for the above linear regression problem, compared with the batch gradient descent, the stochastic gradient descent solution will be the optimal solution?(1) Batch gradient
the basic framework of machine learning:
Model, target (cost function), optimization algorithm
STEP1: For a problem, we need to first establish a model, such as regression or classification model;
Step2: The cost function of the model is established by the minimum classification error, maximum likelihood or maximum posterior probability;
Step3: Solving the optimization problem
A. If there is an analytic solution to the optimization function, it is pos
1. OverviewIn the optimization problem of machine learning, the gradient descent method and Newton method are two common methods to find the extremum of convex function, they are all in order to obtain the approximate solution of the objective function. The aim of the gradient descent is to solve the minimum value of t
gradient descent methods ①stochastic descent random gradient descentQuite unstable, try to turn the study rate down a little bit.The speed is fast, the effect and the stability are poor, need very small study rate②mini-batch descent small batch
learning combat" in p82-83 gives an improved strategy, the learning rate is gradually declining, but not strictly down, part of the code is: For J in Range (Numiter): For I in range (m): alpha = 4/(1.0+j+i) +0.01 so Alpha decreases 1/(j+i) every time, and when J 3. Can the random gradient drop find the value that minimizes the cost function? Not necessarily, but as the number of iterations increases, it will hang around the optimal solution, but this
This paper uses two-dimensional linear fitting as an example to introduce three methods: Batch gradient descent, random gradient descent, and small batch gradient descent.
The dataset
Y.3. Assumption function (hypothesis functions): In supervised learning, in order to fit the input sample, the hypothetical function used is recorded as hθ (x). For example, for samples (xi,yi) (i=1,2,... N), the fitting function can be used as follows: hθ (x) =θ0+θ1x.4. Loss function (loss functions): In order to evaluate the good or bad fit of the model, the loss function is usually used to measure the degree of fitting. The minimization of the loss function means that the fitting degree is t
Gradient descent is a classical common method of minimizing risk function/loss function, and the following summarizes the similarities and differences of three gradient descent algorithms. 1, Batch gradient descent algorithm (batc
to be overshoot the minimum.
The closer to the minimum, the slower the descent rate
Convergence: Iteration ends when the difference between the current two iterations is less than a certain value
To solve this bias, the process is as follows:Then the iterative formula for θ becomes:The expression above applies only when the number of samples is only one, so how do I calculate the predictive function when I have a sample of M values? Batc
regression coefficient θ=θ0,
θ1
,...,
partθn
. So, how can you find theta if you have x and y in your hand? In the regression equation, the method to obtain the corresponding optimal regression coefficients is to minimize the sum of squares of errors.The error here refers to the difference between the predicted Y value and the tru
FITTING A MODEL VIA closed-form equations VS. GRADIENT Descent vs STOCHASTIC GRADIENT descent vs Mini-batch learning. What's the difference?In order to explain the differences between alternative approaches to estimating the parameters of a model, let's take a l Ook at a concrete example:ordinary Least squares (OLS)
gradient descent
Before we learn more about the gradient descent algorithm, let's look at some of the relevant concepts.
1. Step size (Learning rate): The STRIDE length determines how long each step progresses in the negative direction of the gradient during the
,...,
partθn
. So, how do you find theta when there are X and y in your hand? In the regression equation, the method of finding the best regression coefficients corresponding to the characteristics is the sum of the squares of minimizing errors. The error here is to predict the difference between the Y value and the true Y value, and using the simple summation of the error will make th
converge or even diverge. .One thing worth noting:As we approach the local minimum, the guide values will automatically become smaller, so the gradient drop will automatically take a smaller amplitude, which is the practice of gradient descent. So there's actually no need to reduce the alpha in addition, we need a fixed (constant) learning rate α. 4.
Machine Learning (1) gradient descent (gradient descent)
Inscription: Recently, I have been studying Andrew Ng's machine learning, so I have taken these notes.
Gradient Descent is a linear
function.Here we can think of the error function as follows:This error estimation function is to go to the sum of the estimated value of x (i) and the squared sum of the true value Y (i) as the error estimation function, and the 1/2 in front of it is for the sake of derivation, the coefficient is gone.As for why Squared is chosen as the error estimation function, the source of the formula is explained from the perspective of probability distribution in the following handout.How to adjust θ so t
Always thought that some algorithms have been understood, until recently found that the gradient decline are not understood.1 The problem leadsFor the linear regression mentioned in the previous article, first a feature θ1,θ0 is biased, and the last error function is listed as shown:Manual SolverThe goal is to optimize J (θ1), get it minimized, X is Y (i), given
x (i) and the squared sum of the true value Y (i) as the error estimation function, and the 1/2 in front of it is for the sake of derivation, the coefficient is gone.As for why Squared is chosen as the error estimation function, the source of the formula is explained from the perspective of probability distribution in the following handout.How to adjust θ so that J (θ) obtains the minimum value there are many methods, including the least squares (min square), is a completely mathematical descri
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