(PECL trader >= 0.2.0)
trader_minus_dm — Minus Directional Movement
$high
, array $low
[, int $timePeriod
] ) : array
high高价，浮点数数组。
low低价，浮点数数组。
timePeriodNumber of period. Valid range from 2 to 100000.
Returns an array with calculated data or false on failure.