LEARNING APPARATUS, INFERENCE APPARATUS, INFERENCE SYSTEM, LEARNING METHOD, INFERENCE METHOD, AND NON-TRANSITORY COMPUTER-READABLE STORAGE MEDIUM

An apparatus calculates a positive pair similarity between a first feature vector of an image and a second feature vector associated with the same label as a label of the image, calculates a negative pair similarity between the first feature vector and a third feature vector associated with a label different from the label of the image, calculates a loss value with respect to the positive pair similarity lower than a threshold, calculates a loss value with respect to the negative pair similarity higher than the threshold, and learns a parameter of an feature extractor that decreases the loss values. For calculation one of the loss values, a loss function including a function such that an absolute value of a gradient is larger near a predetermined threshold and is non-zero but smaller even at a point away from the threshold is used.