Add other integration methods to the example

We have: meas, integ, and code model INTEG

examples/various/integrate1.cir

@@ -1,21 +1,33 @@
-Test of integ
+Demonstrate the ngspice integration methods
+* function interg
+* meas ... ... INTEG
+* code model INTEG
 
 i1 0 1 1
 R1 1 2 1
-C1 2 3 1 ic=0
+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
-let int1 = integ(Vm1#branch)
 
+* integrate after the simulation
+let int1 = integ(Vm1#branch)
 plot int1 v(2)
 
 let int2 = integ(v(11))
@@ -24,5 +36,9 @@ 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