1. A method of obtaining a function value of tree based device table model for a circuit simulation, comprising: (a) determining if the current bias voltage point is at least one of inside or outside the last visited leaf partition; (b) at least one of proceeding to step (e), if the bias voltage point is in inside the last visited leaf partition; or, determining if the current partition is in the immediate parent node partition, if the current bias voltage point is outside the last visited leaf partition; (c) at least one of repeating step (b), if the current bias voltage point is not in the parent node partition; or, searching for a child partition of the immediate parent node partition relevant to the current bias voltage point, if the current bias voltage point is in the immediate parent node partition; (d) determining if the child partition is a leaf and repeating step (c) if the child partition is not a leaf and proceeding to step (e) if the child partition is a leaf; and (e) performing multi-linear interpolation.