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Logistic Regression classifier
ML implements logistic regression, which is a probabilistic classification technique. Logistic Regression is a binary classification algorithm which is closely related to Support Vector Machines (SVM). Like SVM, Logistic Regression can be extended to work on multi-class classification problems like digit recognition (i.e. recognizing digitis like 0,1 2, 3,... from the given images). This version of Logistic Regression supports both binary and multi-class classifications (for multi-class it creates a multiple 2-class classifiers). In order to train the logistic regression classifier, Batch Gradient Descent and Mini-Batch Gradient Descent algorithms are used (see [BatchDesWiki]). Logistic Regression is a discriminative classifier (see [LogRegTomMitch] for more details). Logistic Regression is implemented as a C++ class in cv.LogisticRegression.
In Logistic Regression, we try to optimize the training parameter
theta
such that the hypothesis 0 <= h_theta(x) <= 1
is achieved. We
have h_theta(x) = g(h_theta(x))
and g(z)=1/(1+e^(-z))
as the
logistic or sigmoid function. The term "Logistic" in Logistic Regression
refers to this function. For given data of a binary classification
problem of classes 0 and 1, one can determine that the given data
instance belongs to class 1 if h_theta(x) >= 0.5
or class 0 if
h_theta(x) < 0.5
.
In Logistic Regression, choosing the right parameters is of utmost importance for reducing the training error and ensuring high training accuracy:
LearningRate
property. It
determines how fast we approach the solution. It is a positive real
number.Iterations
property. This parameter can be thought as number of
steps taken and learning rate specifies if it is a long step or a
short step. This and previous parameter define how fast we arrive at a
possible solution.Regularization
property. One can specify
what kind of regularization has to be performed by passing one of
regularization kinds to this property.TrainMethod
property as either Batch
or
MiniBatch
. If training method is set to MiniBatch
, the size of the
mini batch has to be to a positive integer set with MiniBatchSize
property.A sample set of training parameters for the Logistic Regression classifier can be initialized as follows:
lr = cv.LogisticRegression();
lr.LearningRate = 0.05;
lr.Iterations = 1000;
lr.Regularization = 'L2';
lr.TrainMethod = 'MiniBatch';
lr.MiniBatchSize = 10;
[LogRegWiki]:
[BatchDesWiki]:
[LogRegTomMitch]:
"Generative and Discriminative Classifiers: Naive Bayes and Logistic Regression" in Machine Learning, Tom Mitchell. Machine Learning
[RenMalik2003]:
"Learning a Classification Model for Segmentation". Proc. CVPR, Nice, France (2003).
Superclasses | handle |
Sealed | false |
Construct on load | false |
LogisticRegression | Creates/trains a logistic regression model |
Iterations | Number of iterations. |
LearningRate | The learning rate of the optimization algorithm. |
MiniBatchSize | Number of training samples taken in each step of Mini-Batch Gradient |
Regularization | Kind of regularization to be applied. |
TermCriteria | Termination criteria of the training algorithm. |
TrainMethod | Kind of training method used to train the classifier. |
id | Object ID |
addlistener | Add listener for event. | |
calcError | Computes error on the training or test dataset | |
clear | Clears the algorithm state | |
delete | Destructor | |
empty | Returns true if the algorithm is empty | |
eq | == (EQ) Test handle equality. | |
findobj | Find objects matching specified conditions. | |
findprop | Find property of MATLAB handle object. | |
ge | >= (GE) Greater than or equal relation for handles. | |
getDefaultName | Returns the algorithm string identifier | |
getLearntThetas | Returns the trained parameters | |
getVarCount | Returns the number of variables in training samples | |
gt | > (GT) Greater than relation for handles. | |
isClassifier | Returns true if the model is a classifier | |
isTrained | Returns true if the model is trained | |
Sealed | isvalid | Test handle validity. |
le | <= (LE) Less than or equal relation for handles. | |
listener | Add listener for event without binding the listener to the source object. | |
load | Loads algorithm from a file or a string | |
lt | < (LT) Less than relation for handles. | |
ne | ~= (NE) Not equal relation for handles. | |
notify | Notify listeners of event. | |
predict | Predicts responses for input samples | |
save | Saves the algorithm parameters to a file or a string | |
train | Trains the statistical model |
ObjectBeingDestroyed | Notifies listeners that a particular object has been destroyed. |