SymAC is a symbolic solver for linear electric networks. It operates similar to a traditional SPICE simulator, in that it solves the network and prints results, however, no numerical but symbolical results (such as vout = 1 / (1 + s * R * C)) are given. For small networks the solving is practically done immediately. The solver can provide insight into small-signal model of complex amplifiers, although the expressions tend to get a bit messy with larger networks. The output of the solver can be copied directly into a octave/MATLAB file (or other tools), only the device values have to be defined. Furthermore, symbolic and numerical device parameters can be combined.

The input netlist is similar to regular SPICE format: The first character identifies the device, any following characters before a space character make up the device name. Then the port list follows and lastly the value of the device (for instance, the voltage for a voltage source).

Nodes are identified by characters (not only numbers), 0 is pre-defined as ground node. Node mapping happens automatically and nodes can be named somewhat arbitrarily: They can be made up by any numbers and characters and additionally they can contain -, :, _ and !.

Component values are single-valued per default, but expressions such as 1 / gm can also be used by surrounding them by curly braces, e.g. {1 / gm}. There are some usage examples in the example circuits in the symAC repository.

The results are displayed with .print statements. Possible access functions are the voltage of a node (V(nodename)), the current of a device (I(instance.port)) or other useful functions as two-port parameters, noise etc. Please check the examples folder in the symAC github repository for more information.

The default netlist is a voltage divider with two resistors R1 and R2. The output from that calculation is something like R2*(R2+R1)^(-1). Try changing R2 (the value at the end of the line, not the device name) to R1, the result then should be 1/2. Then you can also make R2 a multiple of R1 with an expression, like this: {3 * R1}. Now the result should be 0.75.

The solver can linearize a large signal netlist. Currently, there is only basic support for MOSFETs, where every mosfet is replaced by its transconductance and output resistance. For linearized netlists, sources that shoud generate AC signals need to include the property ac=1 in their instantiation. Check the large signal example in the SymAC repository for more information.