# dSij/dW00:: = AxB matrix
# dSij/dW00ab = 1x1
# dSij/dW00ab = for stride positions k,l: EE XPAD[k+a,l+b]

# dout[0,0,i,j] * for stride positions k,l: EE XPAD[k+a,l+b]

n = 0
f = 0
c = 0
xpad = np.pad(x,((0,0),(0,0),(pad,pad),(pad,pad)),'constant',constant_values=(0))
dW00 = np.zeros_like(w[0,0,:,:])
for i in range(0,Hp):
  for j in range(0,Wp):
    dW00_tmp = np.zeros_like(dW00)
    for u in range(0,Hp):
      for v in range(0,Wp):
        for a in range(0,A):
          for b in range(0,B):
            dW00_tmp[a,b] += xpad[n,c,u+a,v+b]
    dW00 += dout[n,f,i,j]* dW00_tmp
dw[f,c,:,:] = dW00