What is the history of Sangaku in Japanese culture;also its relationship to mathematics

Sangaku (算額) are votive tablets offered in shinto shrines (and sometimes in buddhist temples) in Japan. The earliest sangaku found date back to the beginning of the 17th century (a few years before the beginning of the japanese Edo period). The problems featured on the sangaku are typical problems of japanese mathematics (wasan 和算) and often involve many circles which is uncommon in western mathematics. These problems can often be seen as amusing mathematic puzzles (such as the modern Sudoku).
Examples of sangaku: (five photos of the tablets on link)
http://www.sangaku.info/

Sangaku problems, often written "san gaku," are geometric problems of the type found on devotional mathematical wooden tablets ("sangaku") which were hung under the roofs of shrines or temples in Japan during two centuries of schism from the West (Fukagawa and Pedoe 1989). During the time of isolation, Japanese mathematicians developed their own "traditional mathematics," which, in the 1850s, began giving way to Western methods. There were also changes in the script in which mathematics was written and, as a result, few people now living know how to interpret the historic tablets (Kimberling).
http://mathworld.wolfram.com/SangakuProb…

Sangaku or San Gaku (算額; lit. mathematical tablet) are Japanese geometrical puzzles in Euclidean geometry on wooden tablets created during the Edo period (1603-1867) by members of all social classes. The Dutch Japanologist Isaac Titsingh first introduced sangaku to the West when he returned to Europe in the late 1790s after more than twenty years in the Far East.

The Sangaku were painted in color on wooden tablets and hung in the precincts of Buddhist temples and Shinto shrines as offerings to the gods or as challenges to the congregants or publish what question one solved. Many of these tablets were lost during the period of modernization that followed the Edo period, but around nine hundred are known to remain.