numpy/matlab compatibility

[Nicholas Devenish]

On 25/01/2011 20:13, Matt Funk wrote:
> 1) a = rand(10,1)
> 2) Y = a
> 3) mask = Y>  100;
> 4) Y(mask) = 100;
> 5) a = a+Y
>
> Basically i am getting stuck on line 4). I was wondering if it is
> possible or not with python?
> (The above is working matlab code)

I don't understand this matlab code completely (I would expect rand to 
return in the range 0-1, so would expect (Y > 100) to match nothing). 
Nonetheless, to achieve line 4 I believe you are looking for:

 >>> Y[mask] = 100

However, you can also do directly:

 >>> Y[Y>100] = 100

This won't work exactly as you anticipate, because presumably in matlab 
the line 'Y = a' makes a copy of 'a' (it has been a long time since I 
used matlab). In python, Y and a will still refer to the same object, so 
altering Y will also alter a. The *most literal* translation to python 
of your sample is probably:

 >> import numpy
 >> a = numpy.random.rand(10,1)
 >> Y = a.copy()
 >> mask = Y > 100
 >> Y[mask] = 100
 >> a = a + Y