To make the CMOS based schmitt trigger we've used 6 transistors-  3 PMOS and 3 NMOS.
Now according to the circuit diagram all the components should be connected and give ports in inputs and outputs and also in Vdd.

After designing a .cir.out file is created which needed to be edited to .cir as we are are using sky130 Process Design Kit,(PDK) 
so the library should be included with correct path.
And run the file in Command Prompt, this can be also run by selecting Ngspice logo in files.


Following are some of the reasons for showing errors-

1) The path of library is not given properly.
2) Sometimes it can show Fatal Error, to solve this we can use cmd.


[Sometime it takes long time to run, so we must have patience it will run.]