optimize_dparam_demo.cir

Symbolic .param optimization demo (Enhancement-144)
* -------------------------------------------------------------------------
* Enhancement-144 lets `optimize` tune symbolic netlist `.param` values, not
* just alter-reachable device parameters. A `.param` is expanded when the deck
* is parsed, so it cannot be changed with `alter`; instead `-dparam` changes it
* with `alterparam` + a quiet `reset` that re-sources the deck.
*
* Here `rtop` is a `.param` used as R1's value, and `kdiv` is a `.param` used
* inside an expression (R2 = 1k*kdiv). We fit BOTH so that the divider output
* is 0.4 V and the total resistance is 5 k (i.e. i(V1) = -0.2 mA). The unique
* solution is R1 = 3 k, R2 = 2 k, i.e. rtop = 3 k and kdiv = 2, recovered from
* a 1 k / 1 start.
*
*   optimize (-param|-dparam) <name> <init> <lo> <hi> [...]
*            -analysis <cmd> (-minimize <expr> | -target <expr> <val> ...) ...
*
* `-param` = device/instance knob (in place, fast); `-dparam` = symbolic .param
* (re-sourced). The two mix freely. Add -verbose to watch the cost fall.
* -------------------------------------------------------------------------
.param rtop=1k
.param kdiv=1
V1 in 0 dc 1
R1 in out {rtop}
R2 out 0 {1k*kdiv}

.control
optimize -dparam rtop 1k 100 10k -dparam kdiv 1 0.1 10
+        -analysis op
+        -minimize (v(out)-0.4)^2 + (abs(i(v1))-0.2m)^2
+        -maxiter 400 -tol 1e-15
* leave the circuit at the optimum and confirm
op
print v(out) i(v1)
.endc
.end