Step by step evaluation of IR_FILTER
This article shows the step by step evaluation of the operation performed by the IR_FILTER function. To start, let us evaluate run this function with IDL setting all of the parameters to [1,1,1]:
IDL> x = [1,1,1]
IDL> c = [1,1,1]
IDL> d = [1,1,1]
IDL> result = ir_filter(c,d,x)
IDL> print, result
1.00000 3.00000 7.00000
To understand how IDL comes produces this result, let us evaluate the equation provided in the documentation step by step (in this case d0=1 so it has been dropped it out of the equation):
We can evaluate the first element of y with x[0] and c[0]:
We can now use the first element of y to evaluate the second element:
Now we can use the results of the second and first element to evaluate the third element:
Thus, the result [y1,y2,y3] is [1,3,7] which is the value that is returned by IDL.
Written by DS and Reviewed by MM (3/16/2018)