INTEGER FUNCTION IDAMAX(N,SX,INCX)
 
an integer function that returns the index of the element in a real*8 vector
with the largest absolute value.
 
N      Input, INTEGER N, number of elements in SX.
 
SX     Input, DOUBLE PRECISION SX(N), vector to be searched.
 
INCX   Input, INTEGER INCX, increment between elements of SX.  For contiguous
       elements, INCX = 1.
 
IDAMAX Output, INTEGER IDAMAX, the index of the entry of maximum absolute 
       magnitude.