On 8/30/06, Lars Friedrich <[EMAIL PROTECTED]> wrote:
This is actually a scalar, i.e., a zero dimensional array. N.uint8(200) would give you the same thing, because (200) is a number, not a tuple like (200,). In any case
In [44]:a = array([200], dtype=uint8)
In [45]:a*100
Out[45]:array([32], dtype=uint8)
In [46]:uint8(100)*100
Out[46]:10000
i.e. , the array arithmetic is carried out in mod 256 because Numpy keeps the array type when multiplying by scalars. On the other hand, when multiplying a *scalar* by a number, the lower precision scalars are upconverted in the conventional way. Numpy makes the choices it does for space efficiency. If you want to work in uint8 you don't have to recast every time you multiply by a small integer. I suppose one could demand using uint8(1) instead of 1, but the latter is more convenient.
Integers can be tricky once the ordinary precision is exceeded and modular arithmetic takes over, it just happens more easily for uint8 than for uint32.
Chuck
Hello,
I would like to discuss the following code:
#***start***
import numpy as N
a = N.array((200), dtype = N.uint8)
print (a * 100) / 100
This is actually a scalar, i.e., a zero dimensional array. N.uint8(200) would give you the same thing, because (200) is a number, not a tuple like (200,). In any case
In [44]:a = array([200], dtype=uint8)
In [45]:a*100
Out[45]:array([32], dtype=uint8)
In [46]:uint8(100)*100
Out[46]:10000
i.e. , the array arithmetic is carried out in mod 256 because Numpy keeps the array type when multiplying by scalars. On the other hand, when multiplying a *scalar* by a number, the lower precision scalars are upconverted in the conventional way. Numpy makes the choices it does for space efficiency. If you want to work in uint8 you don't have to recast every time you multiply by a small integer. I suppose one could demand using uint8(1) instead of 1, but the latter is more convenient.
Integers can be tricky once the ordinary precision is exceeded and modular arithmetic takes over, it just happens more easily for uint8 than for uint32.
Chuck
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