DTW Algorithm OCT-file - c++

Question

I am trying to create a Dynamic Time Warping(DTW) function, which will calculate the minimum distance between the two signals provided to it. It is based on the following algorithm,
DTW Algorithm:-
int DTWDistance(s: array [1..n], t: array [1..m]) {
DTW := array [0..n, 0..m]
w := abs(n-m)// adapt window size (*)
for i := 0 to n
for j:= 0 to m
DTW[i, j] := infinity
DTW[0, 0] := 0
for i := 1 to n
for j := max(1, i-w) to min(m, i+w)
cost := d(s[i], t[j])
DTW[i, j] := cost + minimum(DTW[i-1, j ], // insertion
DTW[i, j-1], // deletion
DTW[i-1, j-1]) // match
return DTW[n, m]
more info DTW Algorithm
Now I was able to create an Octave function of this Algorithm and its working properly.
Octave Function:-
function dtw_distance = dtw2(a,b)
length_a = length(a);
length_b = length(b);
an=zeros(length_a+1,length_b+1);
an(:,:)=9999;
an(1,1)=0;
cost=0;
#Here we have also implemented the window size.
w=abs(length_a-length_b);
for i=1:length_a
for j=max(1,i-w):min(length_b,i+w)
cost=abs(a(i)-b(j));
an(i+1,j+1)=cost+min([an(i,j+1),an(i+1,j),an(i,j)]);
end
end
an;
dtw_distance=an(length_a+1,length_b+1);
Now the computation time of this code increases as the size of argument increases. Hence I am trying to create OCT file which is written in C++ for faster execution.
C++ OCT File:-
#include <octave/oct.h>
octave_idx_type getMax(octave_idx_type a, octave_idx_type b){
return (a>b)?a:b;
}
octave_idx_type getMin(octave_idx_type a, octave_idx_type b){
return (a<b)?a:b;
}
DEFUN_DLD (dtw3, args, , "Find DTW of two Signals With Window")
{
int nargin = args.length();
if (nargin != 2)
print_usage();
else
{
NDArray A = args(0).array_value();
NDArray B = args(1).array_value();
octave_stdout << "Size of A is" << A.length();
octave_stdout << "Size of B is" << B.length();
if (! error_state)
{
octave_idx_type row = A.length()+1;
octave_idx_type col = B.length()+1;
Matrix results (row,col);
for(octave_idx_type i = 0; i <= row ; i++)
{
for(octave_idx_type j=0; j<= col ; j++)
{
results(i,j)=9999;
}
}
octave_stdout << "row col" << results.dim1() << results.dim2() ;
octave_stdout << "row end" << results(row,0) ;
octave_stdout << "col end" << results(0,col) ;
results(0,0)=0;
octave_idx_type win = (row>col)?(row-col):(col-row);
octave_idx_type cost = 0;
for(octave_idx_type i = 1 ; i <= row ; i++)
{
for(octave_idx_type j = getMax(1,i-win) ; j <= getMin(col,i+win) ; j++)
{
cost=(A(i)>B(j))?(A(i)-B(j)):(B(j)-A(i));
results(i,j)= cost + getMin(getMin(results(i-1,j),results(i,j-1)),results(i-1,j-1));
}
}
octave_stdout << "Ans is: " << results(row,col);
return octave_value(results(row,col));
}
}
}
Sample Input/Output
Input - Arg1: [1 2 3 4 5] , Arg2: [1 2 3 4 5 6 7]
Output:
For Octave Function: Ans is 3
For OCT FIle:
* Error in /usr/lib/x86_64-linux-gnu/octave/4.0.0/exec/x86_64-pc-linux-gnu/octave-gui': double free or corruption (!prev): 0x00007f24e81eb0a0 ***
panic: Aborted -- stopping myself...
*** Error in/usr/lib/x86_64-linux-gnu/octave/4.0.0/exec/x86_64-pc-linux-gnu/octave-gui': malloc(): memory corruption: 0x00007f24e81eb230 *
Input : Arg1 : A=rand(1,221), Args2: B=rand(1,299)
Output:
For Octave Function: Ans is 72.63
For OCT File:
* Error in `/usr/lib/x86_64-linux-gnu/octave/4.0.0/exec/x86_64-pc-linux-gnu/octave-gui': double free or corruption (!prev): 0x00007f57a06ad940 *
panic: Aborted -- stopping myself...
Size of A is221Size of B is299row col222300row end9999col end9999Ans is:1 attempting to save variables to 'octave-workspace'...
save to 'octave-workspace' complete
Aborted (core dumped)
My Problem:
First of all what is this double free corruption error I am getting when using OCT files?
The answer for Octave file and OCT file is different, whats the error in OCT file which is causing this?
Thank you.

Answer 1

First, you should read how to debug oct files (http://wiki.octave.org/Debugging_Octave#Debugging_oct-files)
Then you'll find this part:
Matrix results (row,col);
for(octave_idx_type i = 0; i <= row ; i++)
{
for(octave_idx_type j=0; j<= col ; j++)
{
results(i,j)=9999;
}
}
The Matrix result has dimension row, col but you are writing until i<=row and j<=col which is 1 beyond bounds. Try i<row and j<col
There were so many problems in your code which was too much to describe, here my changes. I've replaces some functions which buildt-in functions:
#include <octave/oct.h>
DEFUN_DLD (dtw3, args, , "Find DTW of two signals with window")
{
int nargin = args.length();
if (nargin != 2)
print_usage();
Matrix A = args(0).array_value();
Matrix B = args(1).array_value();
octave_stdout << "Size of A is " << A.length() << std::endl;;
octave_stdout << "Size of B is " << B.length() << std::endl;
if (! error_state)
{
octave_idx_type n = A.length();
octave_idx_type m = B.length();
Matrix results (n + 1, m + 1);
for(octave_idx_type i = 0; i <= n ; i++)
for(octave_idx_type j = 0; j <= m ; j++)
results(i, j) = octave_Inf;
results(0, 0) = 0;
octave_idx_type win = abs (n-m);
double cost = 0;
for(octave_idx_type i = 1 ; i <= n ; i++)
for(octave_idx_type j = std::max(1, i-win) ; j <= std::min(m, i+win) ; j++)
{
cost = abs(A(i-1) - B(j-1));
results(i, j) = cost + std::min(std::min(results(i-1,j),results(i,j-1)),results(i-1,j-1));
}
//octave_stdout << results << std::endl;
return ovl(results(n, m));
}
}