difficulty in matlab to python code conversion

Question

I am converting matlab code to python code

function Xn = ReSampleCurve(X,N)

    [n,T] = size(X);
    del(1) = 0;
    for r = 2:T
        del(r) = norm(X(:,r) - X(:,r-1));
    end
    cumdel = cumsum(del)/sum(del);   

    newdel = [0:N-1]/(N-1);

    for j=1:n
        Xn(j,:) = interp1(cumdel,X(j,1:T),newdel,'linear');
    end

I want to convert this into python code

The input values are :

X = [[-9.035250067710876, 7.453250169754028, 33.34074878692627], [-6.63700008392334, 5.132999956607819, 31.66075038909912],[-5.1272499561309814, 8.251499891281128, 30.925999641418457], [-5.1272499561309814, 8.251499891281128, 30.925999641418457]]
N = 200

can anyone explains me what these lines do?

    del(1) = 0;
    for r = 2:T
        del(r) = norm(X(:,r) - X(:,r-1));

you can always try freemat.sourceforge.net and run the matlab-code to see for yourself... — Fredrik Pihl
– Fredrik Pihl, Commented Jan 9, 2014 at 11:27

Dennis Jaheruddin · Accepted Answer · 2014-01-09 14:33:23Z

1

For what it is worth, here is the vectorized way to get del(2:end) in Matlab, perhaps this makes more sense to you:

sqrt(sum(diff(M,1,2).^2))

answered Jan 9, 2014 at 14:33

Dennis Jaheruddin

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Luke · Accepted Answer · 2014-01-09 15:41:30Z

1

del is an array in the MATLAB code. So del(1) = 0 is equivalent to del_list = [0] (MATLAB arrays a 1-indexed, del is a reserved word in python).

In the for loop, this is equivalent to:

for r in range(1,T):
    del_list.append(norm(X[:,r] - X[:,r-1]))

The above won't work in pure python (array subtraction won't work). You'd have to add in numpy or numeric) - but hopefully you get the idea.

edited Jan 9, 2014 at 15:41

answered Jan 9, 2014 at 11:53

Luke

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