I have been using sage in my research recently. I am not sure which part is wrong but the following code gives the wrong results. The code is long, but I think you may only need to read the last four rows to understand my question. All the rows before that generate a matrix D where the columns are the cycles of the complete graph K_5 (each cycle is a vector in Z^10, 10 is the number of edges.) Then I produce a linear matroid from D and calculate T(2,0) using tutte_polynomial(). The weird thing is that the result is an odd number, which is impossible because the Tutte polynomial has no constant term. The more weird thing is that if I repeat the order again, I get a different result. If I run the code for the graph K_4, nothing is wrong, which is why I need to give the complete code. The code is run by CoCalc.

```
import numpy as np
from sage.matroids.advanced import *
graph=graphs.CompleteGraph(5)
g = graph.to_directed()
allcycles=g.all_simple_cycles()
nv=g.order() #nv is number of vertices
ne=nv*(nv-1)/2 #ne is the number of edges
ncycle=(len(allcycles)-g.size()/2)/2 #ncycle is number of simple cycles
def cycle(array): #array is a cycle in vertices notation eg. [0,1,2,3,0]
l=len(array)-1 #l is the length of the cycle
if l<=2:
return(False)
C=np.zeros(nv*(nv-1)/2) #C is to be a cycle in Z^E
for X in range(l):
i=array[X]+1
j=array[X+1]+1
if i<j:
C[(2*nv-i)*(i-1)/2+j-i-1]=1
else:
C[(2*nv-j)*(j-1)/2+i-j-1]=-1
return(C)
D=np.zeros((ne,ncycle*2)) #D is all directed cycles
X=0
for list in allcycles:
array=np.array(list)
if len(array)>3:
D[:,X]=cycle(array).transpose()
X=X+1
for X in range(ncycle): #reduce D so that D is all cycles with one orientation
positivecolumn=D[:, X]
Y=X+1
while (D[:, Y]+positivecolumn).any()!=0:
Y=Y+1
D=np.delete(D, Y, 1)
print(D)
M=Matroid(Matrix(D))
print("M.tutte_polynomial(2,0)=", M.tutte_polynomial(2,0))
print("M.tutte_polynomial(2,0)=", M.tutte_polynomial(2,0))
```

The results are

[[ 1. 1. 1. 0. 0. 0. 0. 0. 0. 0. 1. 1. 1. 1. 1. 1. 0. 0. 0. 0. 0. 0. 0. 0. 0. 1. 1. 1. 1. 1. 1. 0. 0. 0. 0. 0. 0.] [-1. 0. 0. 1. 1. 0. 0. 0. 0. 0. 0. 0. -1. 0. -1. 0. 1. 1. 1. 1. 0. 0. 0. 0. 0. 0. 0. 0. -1. 0. -1. 1. 1. 1. 1. 0. 0.] [ 0. -1. 0. -1. 0. 1. 0. 0. 0. 0. -1. 0. 0. 0. 0. -1. -1. 0. 0. -1. 1. 1. 0. 0. 0. 0. -1. 0. 0. -1. 0. 0. -1. 0. -1. 1. 1.] [ 0. 0. -1. 0. -1. -1. 0. 0. 0. 0. 0. -1. 0. -1. 0. 0. 0. -1. -1. 0. -1. -1. 0. 0. 0. -1. 0. -1. 0. 0. 0. -1. 0. -1. 0. -1. -1.] [ 1. 0. 0. 0. 0. 0. 1. 1. 0. 0. 1. 1. 0. 0. 0. 0. -1. -1. 0. 0. 0. 0. 1. 1. 0. 1. 1. 0. 0. 0. 0. -1. -1. 0. 0. 1. -1.] [ 0. 1. 0. 0. 0. 0. -1. 0. 1. 0. 0. 0. 1. 1. 0. 0. 1. 0. 0. 0. -1. 0. 0. -1. 1. 0. 0. 1. 1. 0. 0. 1. 0. -1. 1. -1. 0.] [ 0. 0. 1. 0. 0. 0. 0. -1. -1. 0. 0. 0. 0. 0. 1. 1. 0. 1. 0. 0. 1. 0. -1. 0. -1. 0. 0. 0. 0. 1. 1. 0. 1. 1. -1. 0. 1.] [ 0. 0. 0. 1. 0. 0. 1. 0. 0. 1. 1. 0. -1. 0. 0. 0. 0. 0. 1. 0. 0. -1. 1. 0. -1. 1. 0. -1. 0. 1. -1. 0. 0. 1. 0. 0. -1.] [ 0. 0. 0. 0. 1. 0. 0. 1. 0. -1. 0. 1. 0. 0. -1. 0. 0. 0. 0. 1. 0. 1. 0. 1. 1. 0. 1. 1. -1. -1. 0. 0. 0. 0. 1. 1. 0.] [ 0. 0. 0. 0. 0. 1. 0. 0. 1. 1. 0. 0. 0. 1. 0. -1. 0. 0. 1. -1. 0. 0. 1. -1. 0. 1. -1. 0. 1. 0. -1. 1. -1. 0. 0. 0. 0.]] M.tutte_polynomial(2,0)= 46229 M.tutte_polynomial(2,0)= 52640