Finding Matching Nested Parentheses in a String

If the location of a closed or opened parenthesis is known in a string, could you share a code that finds its matching parenthesis in forward or reverse direction of a general purpose equation that has many nested parentheses?

[per isakson]

See http://stackoverflow.com/questions/133601/can-regular-expressions-be-used-to-match-nested-patterns and http://www.regular-expressions.info/balancing.html