1. A method of evaluating precision of output data based on error propagation comprising: performing numerical differentiation using input data in data processing, and obtaining a Jacobian matrix of the data processing; estimating variance-covariance of errors of the input data, and obtaining an error matrix of the input data; and calculating an error matrix from the Jacobian matrix and the error matrix of the input data, the error matrix representing variance-covariance of errors of output data.