Demonstrate the ngspice integration methods
* function interg
* meas ... ... INTEG
* code model INTEG

i1 0 1 1
R1 1 2 1
C1 2 3 1
Vm1 3 0 0
.ic v(2) = 0

v2 11 0 dc 0 sin (0 1 2)

v3 31 0 dc 0 pulse (0 1 0.1 0.1 0.1 0.1 0.6)

* integrate during transient simulation
V4 in 0 dc 0 pwl (0 0 1 1)
aint in out int_in
.model int_in int(in_offset=0.0 gain=1.0
+ out_lower_limit=-1e12 out_upper_limit=1e12
+ limit_range=1e-9 out_ic=0.0)

.tran 0.01 1

.control
run
display

* integrate after the simulation
let int1 = integ(Vm1#branch)
plot int1 v(2)

let int2 = integ(v(11))
plot v(11) int2

let int3 = integ(v(31))
plot v(31) int3

plot in out
* get the integral value of a vector section
meas tran yint INTEG v(out) from=0.4 to=0.6

.endc
.end