1. A computer-implemented method for modeling a circuit including a resistive random access memory (RRAM) cell in a computer system programmed to perform the method, the method comprising: implementing in the computer system, a circuit simulation environment; displaying on a display of the computer system within the circuit simulation environment, a circuit including at least one RRAM cell, the RRAM cell being associated with a first internal state variable; retrieving from a memory of the computer system within the circuit simulation environment, a sub-circuit module compatible with the circuit simulation environment, that represents behavior of the RRAM cell comprising a first component that corresponds to a formula for determining the first internal state variable; determining in the computer system within the circuit simulation environment, a characteristic of the RRAM cell within the circuit in response to the sub-circuit module compatible with the circuit simulation environment by solving the formula for the first internal state variable and obtaining a value representing the characteristic of the RRAM cell; updating the display of the computer system to include at least the value representing the characteristic of the RRAM cell; receiving in the computer system within the circuit simulation environment, modifications to the circuit to form an adjusted circuit in response to the characteristic of the circuit; and storing in the memory of the computer system, the adjusted circuit.