krylov need a good starting point, try nlsolver see if it is the same

fixedpoint.py

@@ -92,7 +92,7 @@ if __name__=='__main__':
     import time
     torch.manual_seed(42)
     d = 2
-    chi = 20
+    chi = 40
     device = 'cpu'
     dtype = torch.float64
 
@@ -104,7 +104,7 @@ if __name__=='__main__':
     T[1, 0, 0, 0] = 1.0 
     
     ctmrg = CTMRG.apply
-    C, E = ctmrg(T, chi, 100)
+    C, E = ctmrg(T, chi, 1000, 1E-6)
 
     x = torch.cat([C.view(-1), E.view(-1)]).numpy()
 
@@ -116,5 +116,5 @@ if __name__=='__main__':
         return torch.cat([C.view(-1), E.view(-1)]).numpy() - x 
 
     from scipy import optimize
-    sol = optimize.root(fun, x, method='krylov', options={'fatol':1E-12, 'disp': True})
+    sol = optimize.root(fun, x, method='krylov', options={'fatol':1E-13, 'disp': True, 'jac_options':{'method': 'lgmres'} })
     print (sol)