I am a newbie and I am trying to use the simulator to find the operating point on a simple circuit, which is supposed to generate a square wave on pin 3. Can anybody can please point me in the right direction? project name: led-matrix-tester **SPICE NETLIST** SquareWave_sim ``` V1 +5V GND  5V R4 R4_1 R3_1  2M R3 R3_1 +5V  1k C4 GND C4_2  10n C3 GND R4_1  50n .param pi = 3.141593 .func LIMIT(x, y, z) {min(max(x, min(y, z)), max(z, y))} .func PWR(x,a) {(MAX(ABS(x), 1e-313))**a} .func PWRS(x,a) {sgn(x) * PWR(x,a)} .func stp(x) {u(x)} .func log10(x) {ln(x)/ln(10)} .func SQRT(x) {(MAX(x, 1e-313))**0.5} .func INT(x) {sgn(x)*floor(ABS(x))} .func URAMP(x) {max(x,0)} .func POW(x,a) + {(((a-(int(a)))==0)||(sgn(x)>=0))*( max(exp(ln(uramp(x))*a),0) + + (2*(0.5-ABS((int(a))-2*int(a/2))))*max(exp(ln(uramp(-1*x))*a),0) )} .control probe V(VOLPROBE1) quit .endc .END ``` **SIMULATION REPORT** ``` Circuit: gooduntitled Doing analysis at TEMP = 27.000000 and TNOM = 27.000000 Warning: singular matrix:  check nodes c4_2 and c4_2 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 c4_2 and c4_2 Warning: Dynamic gmin stepping failed Note: Starting source stepping Warning: singular matrix:  check nodes c4_2 and c4_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 c4_2 and c4_2 Warning: singular matrix:  check nodes c4_2 and c4_2 Warning: source stepping failed DC solution failed - Last Node Voltages ------------------ Node                                   Last Voltage        Previous Iter ----                                   ------------        ------------- +5v                                               0                    0 r4_1                                              0                    0 r3_1                                              0                    0 c4_2                                              0                    0 v1#branch                                         0                    0 doAnalyses: iteration limit reached op simulation(s) aborted Error(parse.c--checkvalid): volprobe1: no such vector. ngspice-26 done ```