Provided are a computer program product, a learning apparatus and a learning method. The method includes calculating, by a processor, a first propagation value that is propagated from a propagation source node to a propagation destination node in a neural network including a plurality of nodes, based on node values of the propagation source node at a plurality of time points and a weight corresponding to passage of time points based on a first attenuation coefficient. The method further includes updating, by the processor, a first update parameter, which is used for updating the first attenuation coefficient, by using the first propagation value. The method also includes updating, by the processor, the first attenuation coefficient by using the first update parameter and an error of the node value of the propagation destination node.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A learning method comprising: calculating, by a processor, a first propagation value that is propagated from a propagation source node to a propagation destination node in a neural network including a plurality of nodes, based on node values of the propagation source node at a plurality of time points and a weight corresponding to passage of time points based on a first attenuation coefficient; updating, by the processor, a first update parameter, which is used for updating the first attenuation coefficient, by using the first propagation value; and updating, by the processor, the first attenuation coefficient by using the first update parameter and an error of the node value of the propagation destination node. 2. The learning method according to claim 1, wherein the updating of the first update parameter includes updating the first update parameter based on a value obtained by calculating a product of the first update parameter at a previous time point and the first attenuation coefficient and adding the first propagation value to the product. 3. The learning method according to claim 2, wherein the updating of the first attenuation coefficient includes updating the first attenuation coefficient further based on a first weight for weighting the first propagation value propagated from the propagation source node to the propagation destination node. 4. The learning method according to claim 2, wherein the updating of the first attenuation coefficient includes calculating an update amount of the first attenuation coefficient based on a learning rate. 5. The learning method according to claim 1, wherein the updating of the first attenuation coefficient includes determining whether to update the first attenuation coefficient based on a random number. 6. The learning method according to claim 1, wherein the first attenuation coefficient is used in common for sets that are each formed by one of a plurality of the propagation source nodes and one of a plurality of the propagation destination nodes, the updating of the first update parameter includes updating the first update parameter for each set of the propagation source nodes and the propagation destination nodes, and the updating of the first attenuation coefficient includes updating the first attenuation coefficient by using the first update parameter for each set of the propagation source nodes and the propagation destination nodes and the error of the node value of each of the propagation destination nodes. 7. The learning method according to claim 1, wherein the first attenuation coefficient is allocated to each of a plurality of the propagation source nodes, the updating the first update parameter includes updating the first update parameter for each set of the propagation source nodes and the propagation destination nodes, and the updating of the first attenuation coefficient includes updating the first attenuation coefficient allocated to one propagation source node, by using the first update parameter for sets that are each formed by the one propagation source node and a propagation destination node from among the plurality of propagation destination nodes and the error of the node value of each propagation destination node. 8. The learning method according to claim 1, wherein the first attenuation coefficient is allocated to each of a plurality of sets that are each formed by one of a plurality of the propagation source nodes and one of a plurality of the propagation destination nodes, the updating of the first update parameter includes updating the first update parameter for each set of the propagation source nodes and the propagation destination nodes, and the updating of the first attenuation coefficient includes updating the first attenuation coefficient allocated to a set of one propagation source node and one propagation destination node, by using the first update parameter for the one propagation source node and the one propagation destination node and the error of the node value of the one propagation destination node. 9. The learning method according to claim 1, comprising: calculating a second propagation value that is propagated from the propagation source node to the propagation destination node, based on values of the propagation source node at a plurality of time points and a weight corresponding to passage of time points based on a second attenuation coefficient; updating a second update parameter, which is used for updating the second attenuation coefficient, by using the second propagation value; and updating the second attenuation coefficient by using the second update parameter and an error of the value of the propagation destination node. 10. The learning method according to claim 9, wherein a propagation value based on a weighted sum of the first propagation value and the second propagation value is propagated from the propagation source node to the propagation destination node. 11. The learning method according to claim 9, wherein the updating of the second update parameter includes updating the second update parameter based on a value obtained by calculating the product of the second update parameter at a previous time point and the second attenuation coefficient and adding the second propagation value and the node value of the propagation source node to the product. 12. The learning method according to claim 1, comprising: sequentially acquiring input data at each time point from time-series input data; shifting each node value of an input layer including a plurality of the propagation destination nodes to a plurality of the propagation source nodes every time the input data is acquired; inputting a plurality of node values included in the input data that is acquired next into the input layer included the plurality of propagation destination nodes; and calculating a probability of the time-series input data occurring or a probability of the input data acquired next occurring, based on a weighted sum obtained by weighting the node values of the plurality of propagation destination nodes with the first propagation value propagated to each of the plurality of propagation destination nodes. 13. A computer program product comprising a non-transitory computer readable storage medium having program instructions embodied therewith, the program instructions executable by a computer to cause the computer to perform a method, the method comprising: calculating, by a processor, a first propagation value that is propagated from a propagation source node to a propagation destination node in a neural network including a plurality of nodes, based on node values of the propagation source node at a plurality of time points and a weight corresponding to passage of time points based on a first attenuation coefficient; updating, by the processor, a first update parameter, which is used for updating the first attenuation coefficient, by using the first propagation value; and updating, by the processor, the first attenuation coefficient by using the first update parameter and an error of the node value of the propagation destination node. 14. The computer program product according to claim 13, wherein the method further comprises performing: the updating of the first update parameter by further including updating the first update parameter based on a value obtained by calculating a product of the first update parameter at a previous time point and the first attenuation coefficient and adding the first propagation value to the product. 15. The computer program product according to claim 13, wherein the method further comprises performing: the updating of the first attenuation coefficient by further including updating the first attenuation coefficient further based on a first weight for weighting the first propagation value propagated from the propagation source node to the propagation destination node. 16. The computer program product according to claim 13, wherein the method further comprises: sequentially acquiring input data at each time point from time-series input data; shifting each node value of an input layer including a plurality of the propagation destination nodes to a plurality of the propagation source nodes every time the input data is acquired; inputting a plurality of node values included in the input data that is acquired next into the input layer included the plurality of propagation destination nodes; and calculating a probability of the time-series input data occurring or a probability of the input data acquired next occurring, based on a weighted sum obtained by weighting the node values of the plurality of propagation destination nodes with the first propagation value propagated to each of the plurality of propagation destination nodes. 17. A learning apparatus for learning a model corresponding to time-series input data, comprising: a processor configured to: calculate a first propagation value that is propagated from a propagation source node to a propagation destination node in a neural network including a plurality of nodes, based on node values of the propagation source node at a plurality of time points and a weight corresponding to passage of time points based on a first attenuation coefficient; update a first update parameter, which is used for updating the first attenuation coefficient, by using the first propagation value; and update the first attenuation coefficient by using the first update parameter and an error of the node value of the propagation destination node. 18. The learning apparatus according to claim 17, wherein the processor is further configured to perform the update of the first update parameter by further including an update of the first update parameter based on a value obtained by calculation of a product of the first update parameter at a previous time point and the first attenuation coefficient and addition of the first propagation value to the product. 19. The learning apparatus according to claim 17, wherein the processor is further configured to perform the update of the first attenuation coefficient by further including an update of the first attenuation coefficient further based on a first weight for weighting the first propagation value propagated from the propagation source node to the propagation destination node. 20. The learning apparatus according to claim 17, wherein the processor is further configured to: sequentially acquire input data at each time point from time-series input data; shift each node value of an input layer including a plurality of the propagation destination nodes to a plurality of the propagation source nodes every time the input data is acquired; input a plurality of node values included in the input data that is acquired next into the input layer including the plurality of propagation destination nodes; and calculate a probability of the time-series input data occurring or a probability of the input data acquired next occurring, based on a weighted sum obtained by weighting the node values of the plurality of propagation destination nodes with the first propagation value propagated to each of the plurality of propagation destination nodes.