Hi,I wrote a code for solving a finite element problem.for loop fourth times generates k(a matrix) .i want to sum the k together,but i can’t.what change i have to make in for loop?

```
import numpy as np
#Coordinate and Thickness
x,y,t=[1,1,2,2],[0,1,1,0],1
# Material Property,Elasticitycondition 1 is Plane Strain/Elasticitycondition 0 is Plane Stress
E,P,Elasticitycondition=210,0.25,0
#Define coordinate matrix and gaussian points(1 points),counter clockwise direction
c=np.vstack([x,y])
ke,te=[-0.577,-0.577,0.577,0.577],[-0.577,0.577,0.577,-0.577]
# D Matrix Calculation
cof1=E/((1+P)*(1-2*P))
cof2=E/(1-(P**2))
K1=[[1-P,P,0],[P,P,0],[0,0,(1-2*P)/2]]
K2=[[1,P,0],[P,1,0],[0,0,(1-P)/2]]
D=np.zeros((3,3))
if Elasticitycondition==1:
D+=K1
D*=cof1
elif Elasticitycondition==0:
D+=K2
D*=cof2
#Calculation Strain and stiffness matrix
for i in range(len(ke)):
k=np.zeros((8,8))
df=np.zeros((4,2))
df+=[[-1+te[i],-1+ke[i]]
,[1-te[i],-1-ke[i]]
,[1+te[i],1+ke[i]]
,[-1-te[i],1-ke[i]]]
df*=0.25
j=c@df
df2=df@np.linalg.inv(j)
b=[[df2[0,0],0,df2[1,0],0,df2[2,0],0,df2[3,0],0]
,[0,df2[0,1],0,df2[1,1],0,df2[2,1],0,df2[3,1]]
,[df2[0,1],df2[0,0],df2[1,1],df2[1,0],df2[2,1],df2[2,0],df2[3,1],df2[3,0]]]
k=[t*np.linalg.det(j)]*np.transpose(b)@D@b
print(k)
```