My knowledge of IDL is not what it used to be, I had to research a little. The operator ">" in IDL is not an equivalent of python (or other languages). It stablishes a maximum, anything above it will be set to that value. Same goes for "<", obviously, it sets a minimum.
dk2 = (k2arr((ind2+1) < nsteps) - k2arr(ind2-1) > 0)) where k2arr is 266 and ind2 is (266,266) is equivalent to saying:
- (ind2+1 < nsteps) take ind2+1 and, in any place that ind2+1
is greater than nsteps, replace by nsteps.
- (ind2-1 > 0) take ind2-1 and, in any place that ind2-1 is
less than zero, put zero instead.
The tricky part is now. k2arr (266,) is evaluated for each of the rows of (ind2+1) and (ind2-1), meaning that if (ind2+1 < nsteps) = [1,2,3,...,nsteps-1, nsteps, nsteps] the k2arr will be evaluated for exactly that 266 times, one on top of the other, with the result being (266,266) array.
And NOW I remember why I stopped programming in IDL!