how can I add data to an already trained model

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Thanks for your answer.I trained A-Z 0-9 for 180 samples and accuracy is 90%. If I train 36 samples as one group, updated it by parameters "update" in train() 4 times(the same sample).accuracy is under 50%. How can I train the samples one by one and get a good result.

why do you want to do it, that way ? (and what model are you using ?)

I trained model by my samples. I want to updated model using the new training data instead of retrain it. Because it takes too long time.I test this method by some samples. I guess that if I train the model by a full samples or train it by half samples , updated it by the other half, it will be the same result. But I was wrong.I don't understand why and I want to know that my idea is right or not.

again, which ml model are you trying to use ? and where is your code ?

I want to try opencv model in (KNN,Neural,Bayes,SVM) and decide which to use.I find Neural,Bayes have update paramters, just _neural.load("neural.xml") and _neural.train(train_data, train_class, Mat(), Mat(), params, CvANN_MLP::UPDATE_WEIGHTS); I don't know how to upload the code.