| 摘要 |
An approximate value calculating unit is provided for a storage apparatus in which a seek control is performed by speed controlling a head. When a square root arithmetic operation is needed in the calculation of a seek speed target value which is used in the seek control, the approximate value calculating unit divides a range of an input value x serving as a target of the square root arithmetic operation into a plurality of intervals, sets a polynomial of degree N to approximately output a square root {square root over ( x of the input value x as an approximate function every interval, and calculates the square root approximate value of the input value x by selectively using the approximate function corresponding to the interval to which the input value x belongs. Further, according to the range dividing method of the input value x, it is sufficient that the polynomial of degree N or the approximate function by the reference table is prepared only for the basic range, and there is no need to prepare the approximate function which covers the range before the input value x. Even when the square root approximate value for the input value x belonging to the range out of the basic range is obtained by executing the input scale conversion and output scale conversion, the approximate function prepared for the basic range can be used.
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