In some special cases, the constitutive relation simplifies to a function of one variable. This is the case for all linear elements, but also, for example, an ideal diode, which in circuit theory terms is a non-linear resistor, has a constitutive relation of the form . Both independent voltage and independent current sources can be considered non-linear resistors under this definition.
In some special cases the constitutive relation simplifies to a function of one variable This is the case for all linear elements but also for example an ideal diode which in circuit theory terms is a non-linear resistor has a constitutive relation of the form  Both independent voltage and independent current sources can be considered non-linear resistors under this definition