For Problem Set 2, the derivative program, I am confused about how the solution returns the correct answer:
poly_deriv = []
if len(poly)

Question

For Problem Set 2, the derivative program, I am confused about how the solution returns the correct answer: 
 poly_deriv = []
    if len(poly) < 2:
        return [0.0]
    for j in xrange(1, len(poly)):
        poly_deriv.append(float(j * poly[j]))
    return poly_deriv                                                             Specifically, where in the code does the program reduce the exponent by 1?

anonymous · Answer

We would express the polynomial $x^2+4x+5$ would be expressed as
```
[5.0, 4.0, 1.0]
```
The derivative polynomial $2x+4$ would be expressed as
```
[4.0, 2.0]
```
Due to the fact that `xrange(1, len(poly))` will iterate starting at `1`, the constant term at `0` is skipped, and all of the terms are shifted over. This shift is equivalent to reducing the exponent.