>> Can anybody tell me what does this mean:
>>
>> x= a LT total(abs(b))/1e7/NFREE
>>
>> where:
>> b= an array of floating point numbers
>> a= a floating point number
>> NFREE= an integer
>>
> x= a LT (total(abs(b))/1e7/NFREE)
In addition to what David wrote, you may have been asking a
very basic question.
The LT (less-than) operator returns true=1 or false=0, and it is
evaluated for each element in the arrays "a" and the temporary array
David put in parantheses above. So x will be an array of 1s and 0s, 1
wherever the less-than statement is true.
Here are a few examples. The behavior is a little different if either
a or b is scalar, or if a and b have multiple elements but their
lengths do not match.
IDL> print, [1,2,3,4,5] LT [3,3,3,3,3]
1 1 0 0 0 ;-- evaluated element-by-element
IDL> print, [1,2,3,4,5] LT [0,0,10,1,2]
0 0 1 0 0 ;-- similar to the above
IDL> print, [1,2,3,4,5] LT 3
1 1 0 0 0 ;-- all elements are compared to this scalar
IDL> print, [1,2,3,4,5] LT [5,5]
1 1 ;-- only the first two elements are compared
IDL> print, [1,2,3,4,5] LT [3,3,3,3,3,3,3,3]
1 1 0 0 0 ;-- only 5 elements are compared
In the last two examples, where the lengths do not match, the result
has the length of the smaller of the two arrays.
Likewise if the 3 in the third example is replaced with [3], a
one-element array, then the result will only have one element as well.
You'll get this same kind of behavior from the other comparison
operators, GT, EQ, LE, and GE.
M. Katz
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