1779
In this research , we optimize the lattice density distribution using a lattice structure approximation and the gradient method .
 concept or principle: research; engineering feature: lattice density; concept or principle: distribution; engineering feature: lattice structure
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
 Entities: research, lattice density, distribution, lattice structure 
Answer:
 concept or principle: research; engineering feature: lattice density; concept or principle: distribution; engineering feature: lattice structure