Hello, I was trying to simulate this circuit but every time i try i get this message Circuit: gooduntitled Doing analysis at TEMP = 27.000000 and TNOM = 27.000000 Warning: singular matrix:  check nodes u1\_1 and u1\_1 Note: Starting dynamic gmin stepping Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Warning: singular matrix:  check nodes d2\_2 and d2\_2 Warning: Dynamic gmin stepping failed Note: Starting source stepping Warning: singular matrix:  check nodes d2\_2 and d2\_2 Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful gmin step Note: One successful source step Warning: singular matrix:  check nodes d2\_2 and d2\_2 Warning: singular matrix:  check nodes d2\_2 and d2\_2 Warning: source stepping failed Transient solution failed - Last Node Voltages \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- Node                                   Last Voltage        Previous Iter \-\-\-\-                                   \-\-\-\-\-\-\-\-\-\-\-\-        \-\-\-\-\-\-\-\-\-\-\-\-\- xt2_1                                             0                    0 xt2.netr1_1                                       0                    0 xt2_4                                             0                    0 xt2.netr2_1                                       0                    0 r6_1                                              0                    0 u1_3                                              0                    0 volprobe                                          0                    0 r5_2                                              0                    0 r4_1                                              0                    0 r3_1                                              0                    0 d2_3                                              0                    0 r1_1                                              0                    0 r1_2                                              0                    0 gnd                                               0                    0 d2_2                                              0                    0 u1_1                                              0                    0 l.xt2.l2#branch                                   0                    0 l.xt2.l1#branch                                   0                    0 doAnalyses: iteration limit reached tran simulation(s) aborted Error(parse.c--checkvalid): volprobe: no such vector. ngspice-26 done here is the circuit: [https://easyeda\.com/editor\#id=817e5fbef04e4725bb8c6f2c6f4d4b25\|65379c4ec9e14037a2ee8c095c02632a\|3ecee614364641058a34856c27c99156](https://easyeda.com/editor#id=817e5fbef04e4725bb8c6f2c6f4d4b25|65379c4ec9e14037a2ee8c095c02632a|3ecee614364641058a34856c27c99156)