Function calculates wrong value

Nik joung (view profile)

on 14 Nov 2017
Latest activity Edited by Michal Kvasnicka

on 14 Nov 2017

Michal Kvasnicka (view profile)

Hello,
the following function computes the number of binary words of length m and certain weight r (number of ones), which do not contain l consecutive zeros:
if (r==0)
if (m<=l-1)
numberOfStrings = 1;
return
else
numberOfStrings = 0;
return
end
else
tmp = 0;
for j=0:min(m,l-1)
for s=0:r-1
bin1=0;
bin2=0;
if ((m-j)-1-s*l < r-1)
bin1 = 0;
else
bin1 = nchoosek((m-j)-1-s*l,r-1);
end
if ((m-j)-1-(1+s)*l < r-1)
bin2 = 0;
else
bin2 = nchoosek((m-j)-1-(1+s)*l,r-1);
end
tmp = tmp + (-1)^s * nchoosek(r-1,s) * (bin1-bin2);
end
end
numBin = tmp;
end
In the first If-case we consider r=0 (also no ones in the sequences), in the else case we consider weights r >= 1.
I have problems with the case, where no consecutive zeros are allowed in the words (variable l=1). For a certain length m there exists only one possible binary sequence. It is the word with the weight equal to the length (r=m).
For example: m=2 --> possible sequence is 11 (has weight r=2) or for m=8 --> possible sequence is 11111111 (has weight r=8). For all other weights r there don't exists possible sequences (the function should output 0).
Until the word length m = 48 the function seems to work well. With m=48, there exists one word (containing no consecutive zeros) with the weight r=48. For all other weights r it outputs 0.
When I use larger lengths m than 49, the function is not working well anymore. The function outputs the number 1 (for r=49). For all other weights r it should be zero. But if I use r=25, it outputs -2 instead of 0. It gets worser for larger lengths.
Can anyone help me with this problem?

1 Comment

on 14 Nov 2017
Have you used the debugger to look at what is going on line-by-line? It's by far the best way for a function that you know better than anyone else (assuming you wrote it and if you didn't it is even better as a way to understand someone else's function!)

Michal Kvasnicka (view profile)

on 14 Nov 2017
Edited by Michal Kvasnicka

on 14 Nov 2017