python to MATLAB code, lists of numbers and summing

Question

I'm completely new to python and Numpy, and I'm trying to rewrite some python code in MATLAB. In the process I found this line which I don't understand a=np.array(eval(self.param[7]))[0:6].sum(); param is an structure containing 8 arrays something like this :

param[0]=100;  
param[1]=1;  
param[2]=1.5;                     
param[3]=(1,2,3,4);  
param[4]=(1,1,1,1);  
param[5]=10;  
param[6]=(1,0.,1,1,1,0.,0.,0.);  
param[7]=(2,0.,2,3,6,0.,0.,0.);

can someone tell me what does [0:6] and then.sum() do? My thought is a is a sum of all the 7 first element in the param[7], but it does not fit to the whole process.

Simon Gibbons · Accepted Answer · 2015-02-24 10:13:09Z

2

The [0:6] will take the first 6 elements in param[7] producing the array

[2,0.,2,3,6,0.]

Then the .sum() method will sum the elements in that array.

Just a quick note on array slicing in python, the expression x[i:j:k] will take every k^th element from the array x starting at the i^th element, upto but not including the j^th element.

If you miss any of them out then python will you assume that you mean the beginning of the array, the end of the array and 1 respectively. So the slice in your code could be slightly more succinctly written as [:6]

edited Feb 24, 2015 at 10:13

answered Feb 24, 2015 at 10:07

Simon Gibbons

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