Finding the Indicies of the Max/Min in a Multidimensional Array


In a 1-d array in IDL, the maximum or minumum value and the corresponding
index can be found with the max() or min() functions.  For example,

IDL> a = dblarr(5)
IDL> a[2] = 1.d
IDL> amax = max(a,i)
IDL> print,amax,i
       1.0000000	  2

For a multidimensional array max() and min() will still return the maximum 
and minimum values, but index i will be set as if the input array were
"strung out" into one dimension.  For example,

IDL> a = dblarr(5,6,7)
IDL> a[1,2,3] = -1.d
IDL> amin = min(a,i)
IDL> print,amin,i
      -1.0000000         101

I won't attempt to explain where "101" came from, but it is clearly not any
of the indices in "a".  The function array_indices(), however, can give 
us all three indices of the minimum element in "a".  It takes as input the 
array of interest and the 1-d index, which in the above case was i = 101, and 
returns an array containing the multidimensional indices as shown below.

IDL> iarr = array_indices(a,i)
IDL> print,iarr,a[iarr[0],iarr[1],iarr[2]]
           1           2           3
      -1.0000000

There is much more information on max(), min(), and array_indices() in the IDL
documentation.